These functions are declared in the main Allegro header file:

     #include <allegro5/allegro.h>

# About UTF-8 string routines

Some parts of the Allegro API, such as the font rountines, expect Unicode strings encoded in UTF-8. The following basic routines are provided to help you work with UTF-8 strings, however it does not mean you need to use them. You should consider another library (e.g. ICU) if you require more functionality.

Briefly, Unicode is a standard consisting of a large character set of over 100,000 characters, and rules, such as how to sort strings. A code point is the integer value of a character, but not all code points are characters, as some code points have other uses. Unlike legacy character sets, the set of code points is open ended and more are assigned with time.

Clearly it is impossible to represent each code point with a 8-bit byte (limited to 256 code points) or even a 16-bit integer (limited to 65536 code points). It is possible to store code points in a 32-bit integers but it is space inefficient, and not actually that useful (at least, when handling the full complexity of Unicode; Allegro only does the very basics). There exist different Unicode Transformation Formats for encoding code points into smaller code units. The most important transformation formats are UTF-8 and UTF-16.

UTF-8 is a variable-length encoding which encodes each code point to between one and four 8-bit bytes each. UTF-8 has many nice properties, but the main advantages are that it is backwards compatible with C strings, and ASCII characters (code points in the range 0-127) are encoded in UTF-8 exactly as they would be in ASCII.

UTF-16 is another variable-length encoding, but encodes each code point to one or two 16-bit words each. It is, of course, not compatible with traditional C strings. Allegro does not generally use UTF-16 strings.

Here is a diagram of the representation of the word “ål”, with a NUL terminator, in both UTF-8 and UTF-16.

                       ---------------- ---------------- --------------
               String         å                l              NUL
                       ---------------- ---------------- --------------
          Code points    U+00E5 (229)     U+006C (108)     U+0000 (0)
                       ---------------- ---------------- --------------
          UTF-8 bytes     0xC3, 0xA5          0x6C            0x00
                       ---------------- ---------------- --------------
       UTF-16LE bytes     0xE5, 0x00       0x6C, 0x00      0x00, 0x00
                       ---------------- ---------------- --------------

You can see the aforementioned properties of UTF-8. The first code point U+00E5 (“å”) is outside of the ASCII range (0-127) so is encoded to multiple code units – it requires two bytes. U+006C (“l”) and U+0000 (NUL) both exist in the ASCII range so take exactly one byte each, as in a pure ASCII string. A zero byte never appears except to represent the NUL character, so many functions which expect C-style strings will work with UTF-8 strings without modification.

On the other hand, UTF-16 represents each code point by either one or two 16-bit code units (two or four bytes). The representation of each 16-bit code unit depends on the byte order; here we have demonstrated little endian.

Both UTF-8 and UTF-16 are self-synchronising. Starting from any offset within a string, it is efficient to find the beginning of the previous or next code point.

Not all sequences of bytes or 16-bit words are valid UTF-8 and UTF-16 strings respectively. UTF-8 also has an additional problem of overlong forms, where a code point value is encoded using more bytes than is strictly necessary. This is invalid and needs to be guarded against.

In the following “ustr” functions, be careful whether a function takes code unit (byte) or code point indices. In general, all position parameters are in code unit offsets. This may be surprising, but if you think about it, it is required for good performance. (It also means some functions will work even if they do not contain UTF-8, since they only care about storing bytes, so you may actually store arbitrary data in the ALLEGRO_USTRs.)

For actual text processing, where you want to specify positions with code point indices, you should use al_ustr_offset to find the code unit offset position. However, most of the time you would probably just work with byte offsets.

# UTF-8 string types

## ALLEGRO_USTR

    typedef struct _al_tagbstring ALLEGRO_USTR;

Source Code

An opaque type representing a string. ALLEGRO_USTRs normally contain UTF-8 encoded strings, but they may be used to hold any byte sequences, including NULs.

Examples:

- ex_font_multiline.cpp
- nihgui.cpp
- ex_blend.c

## ALLEGRO_USTR_INFO

    typedef struct _al_tagbstring ALLEGRO_USTR_INFO;

Source Code

A type that holds additional information for an ALLEGRO_USTR that references an external memory buffer. You can convert it back to ALLEGRO_USTR via al_ref_info.

See also: al_ref_cstr, al_ref_buffer, al_ref_info and al_ref_ustr.

Examples:

- ex_font_multiline.cpp
- nihgui.cpp
- ex_blend.c

# Creating and destroying strings

## al_ustr_new

    ALLEGRO_USTR *al_ustr_new(const char *s)

Source Code

Create a new string containing a copy of the C-style string `s`. The string must eventually be freed with al_ustr_free.

See also: al_ustr_new_from_buffer, al_ustr_newf, al_ustr_dup, al_ustr_new_from_utf16

Examples:

- nihgui.cpp
- ex_emoji.c
- ex_loading_thread.c

## al_ustr_new_from_buffer

    ALLEGRO_USTR *al_ustr_new_from_buffer(const char *s, size_t size)

Source Code

Create a new string containing a copy of the buffer pointed to by `s` of the given `size` in bytes. The string must eventually be freed with al_ustr_free.

See also: al_ustr_new

Examples:

- ex_utf8.c

## al_ustr_newf

    ALLEGRO_USTR *al_ustr_newf(const char *fmt, ...)

Source Code

Create a new string using a printf-style format string.

Notes:

The “%s” specifier takes C string arguments, not ALLEGRO_USTRs. Therefore to pass an ALLEGRO_USTR as a parameter you must use al_cstr, and it must be NUL terminated. If the string contains an embedded NUL byte everything from that byte onwards will be ignored.

The “%c” specifier outputs a single byte, not the UTF-8 encoding of a code point. Therefore it is only usable for ASCII characters (value <= 127) or if you really mean to output byte values from 128–255. To insert the UTF-8 encoding of a code point, encode it into a memory buffer using al_utf8_encode then use the “%s” specifier. Remember to NUL terminate the buffer.

See also: al_ustr_new, al_ustr_appendf

Examples:

- ex_utf8.c

## al_ustr_free

    void al_ustr_free(ALLEGRO_USTR *us)

Source Code

Free a previously allocated string. Does nothing if the argument is NULL.

See also: al_ustr_new, al_ustr_new_from_buffer, al_ustr_newf

Examples:

- nihgui.cpp
- ex_emoji.c
- ex_loading_thread.c

## al_cstr

    const char *al_cstr(const ALLEGRO_USTR *us)

Source Code

Get a `char *` pointer to the data in a string. This pointer will only be valid while the ALLEGRO_USTR object is not modified and not destroyed. The pointer may be passed to functions expecting C-style strings, with the following caveats:

- ALLEGRO_USTRs are allowed to contain embedded NUL (`'\0'`) bytes. That means `al_ustr_size(u)` and `strlen(al_cstr(u))` may not agree.

- An ALLEGRO_USTR may be created in such a way that it is not NUL terminated. A string which is dynamically allocated will always be NUL terminated, but a string which references the middle of another string or region of memory will not be NUL terminated.

- If the ALLEGRO_USTR references another string, the returned C string will point into the referenced string. Again, no NUL terminator will be added to the referenced string.

See also: al_ustr_to_buffer, al_cstr_dup

Examples:

- nihgui.cpp
- ex_emoji.c
- ex_loading_thread.c

## al_ustr_to_buffer

    void al_ustr_to_buffer(const ALLEGRO_USTR *us, char *buffer, int size)

Source Code

Write the contents of the string into a pre-allocated buffer of the given size in bytes. The result will always be NUL terminated, so a maximum of `size - 1` bytes will be copied.

See also: al_cstr, al_cstr_dup

Examples:

- ex_utf8.c

## al_cstr_dup

    char *al_cstr_dup(const ALLEGRO_USTR *us)

Source Code

Create a NUL (`'\0'`) terminated copy of the string. Any embedded NUL bytes will still be presented in the returned string. The new string must eventually be freed with al_free.

If an error occurs NULL is returned.

See also: al_cstr, al_ustr_to_buffer, al_free

Examples:

- ex_emoji.c
- ex_utf8.c

## al_ustr_dup

    ALLEGRO_USTR *al_ustr_dup(const ALLEGRO_USTR *us)

Source Code

Return a duplicate copy of a string. The new string will need to be freed with al_ustr_free.

See also: al_ustr_dup_substr, al_ustr_free

Examples:

- ex_emoji.c
- ex_utf8.c

## al_ustr_dup_substr

    ALLEGRO_USTR *al_ustr_dup_substr(const ALLEGRO_USTR *us, int start_pos,
       int end_pos)

Source Code

Return a new copy of a string, containing its contents in the byte interval [`start_pos`, `end_pos`). The new string will be NUL terminated and will need to be freed with al_ustr_free.

If necessary, use al_ustr_offset to find the byte offsets for a given code point that you are interested in.

See also: al_ustr_dup, al_ustr_free

Examples:

- ex_emoji.c
- ex_utf8.c

# Predefined strings

## al_ustr_empty_string

    const ALLEGRO_USTR *al_ustr_empty_string(void)

Source Code

Return a pointer to a static empty string. The string is read only and must not be freed.

Examples:

- ex_utf8.c

# Creating strings by referencing other data

## al_ref_cstr

    const ALLEGRO_USTR *al_ref_cstr(ALLEGRO_USTR_INFO *info, const char *s)

Source Code

Create a string that references the storage of a C-style string. The information about the string (e.g. its size) is stored in the structure pointed to by the `info` parameter. The string will not have any other storage allocated of its own, so if you allocate the `info` structure on the stack then no explicit “free” operation is required.

The string is valid until the underlying C string disappears.

Example:

    ALLEGRO_USTR_INFO info;
    ALLEGRO_USTR *us = al_ref_cstr(&info, "my string");

See also: al_ref_buffer, al_ref_ustr

Examples:

- ex_blend.c
- ex_utf8.c
- ex_ttf.c

## al_ref_buffer

    const ALLEGRO_USTR *al_ref_buffer(ALLEGRO_USTR_INFO *info, const char *s, size_t size)

Source Code

Create a string that references the storage of an underlying buffer. The size of the buffer is given in bytes. You can use it to reference only part of a string or an arbitrary region of memory.

The string is valid while the underlying memory buffer is valid.

See also: al_ref_cstr, al_ref_ustr

Examples:

- ex_font_multiline.cpp
- ex_utf8.c

## al_ref_ustr

    const ALLEGRO_USTR *al_ref_ustr(ALLEGRO_USTR_INFO *info, const ALLEGRO_USTR *us,
       int start_pos, int end_pos)

Source Code

Create a read-only string that references the storage of another ALLEGRO_USTR string. The information about the string (e.g. its size) is stored in the structure pointed to by the `info` parameter. The new string will not have any other storage allocated of its own, so if you allocate the `info` structure on the stack then no explicit “free” operation is required.

The referenced interval is [`start_pos`, `end_pos`). Both are byte offsets.

The string is valid until the underlying string is modified or destroyed.

If you need a range of code-points instead of bytes, use al_ustr_offset to find the byte offsets.

See also: al_ref_cstr, al_ref_buffer

Examples:

- nihgui.cpp
- ex_blend.c
- ex_utf8.c

## al_ref_info

    const ALLEGRO_USTR *al_ref_info(const ALLEGRO_USTR_INFO *info)

Source Code

Create a read-only string that references the storage of another ALLEGRO_USTR string that has already been stored in the ALLEGRO_USTR_INFO structure.

The string is valid until the underlying string is modified or destroyed.

See also: al_ref_cstr, al_ref_buffer, al_ref_ustr

# Sizes and offsets

## al_ustr_size

    size_t al_ustr_size(const ALLEGRO_USTR *us)

Source Code

Return the size of the string in bytes. This is equal to the number of code points in the string if the string is empty or contains only 7-bit ASCII characters.

See also: al_ustr_length

Examples:

- nihgui.cpp
- ex_utf8.c

## al_ustr_length

    size_t al_ustr_length(const ALLEGRO_USTR *us)

Source Code

Return the number of code points in the string.

See also: al_ustr_size, al_ustr_offset

Examples:

- ex_blend.c
- ex_emoji.c
- ex_utf8.c

## al_ustr_offset

    int al_ustr_offset(const ALLEGRO_USTR *us, int index)

Source Code

Return the byte offset (from the start of the string) of the code point at the specified index in the string. A zero index parameter will return the first character of the string. If index is negative, it counts backward from the end of the string, so an index of -1 will return an offset to the last code point.

If the index is past the end of the string, returns the offset of the end of the string.

See also: al_ustr_length

Examples:

- ex_blend.c
- ex_emoji.c
- ex_utf8.c

## al_ustr_next

    bool al_ustr_next(const ALLEGRO_USTR *us, int *pos)

Source Code

Find the byte offset of the next code point in string, beginning at `*pos`. `*pos` does not have to be at the beginning of a code point.

Returns true on success, and the value pointed to by `pos` will be updated to the found offset. Otherwise returns false if `*pos` was already at the end of the string, and `*pos` is unmodified.

This function just looks for an appropriate byte; it doesn’t check if found offset is the beginning of a valid code point. If you are working with possibly invalid UTF-8 strings then it could skip over some invalid bytes.

See also: al_ustr_prev

Examples:

- nihgui.cpp
- ex_utf8.c

## al_ustr_prev

    bool al_ustr_prev(const ALLEGRO_USTR *us, int *pos)

Source Code

Find the byte offset of the previous code point in string, before `*pos`. `*pos` does not have to be at the beginning of a code point. Returns true on success, and the value pointed to by `pos` will be updated to the found offset. Otherwise returns false if `*pos` was already at the end of the string, and `*pos` is unmodified.

This function just looks for an appropriate byte; it doesn’t check if found offset is the beginning of a valid code point. If you are working with possibly invalid UTF-8 strings then it could skip over some invalid bytes.

See also: al_ustr_next

Examples:

- nihgui.cpp
- ex_utf8.c
- ex_logo.c

# Getting code points

## al_ustr_get

    int32_t al_ustr_get(const ALLEGRO_USTR *ub, int pos)

Source Code

Return the code point in `ub` beginning at byte offset `pos`.

On success returns the code point value. If `pos` was out of bounds (e.g. past the end of the string), return -1. On an error, such as an invalid byte sequence, return -2.

See also: al_ustr_get_next, al_ustr_prev_get

Examples:

- ex_utf8.c
- ex_ttf.c

## al_ustr_get_next

    int32_t al_ustr_get_next(const ALLEGRO_USTR *us, int *pos)

Source Code

Find the code point in `us` beginning at byte offset `*pos`, then advance to the next code point.

On success return the code point value. If `pos` was out of bounds (e.g. past the end of the string), return -1. On an error, such as an invalid byte sequence, return -2. As with al_ustr_next, invalid byte sequences may be skipped while advancing.

See also: al_ustr_get, al_ustr_prev_get

Examples:

- ex_utf8.c

## al_ustr_prev_get

    int32_t al_ustr_prev_get(const ALLEGRO_USTR *us, int *pos)

Source Code

Find the beginning of a code point before byte offset `*pos`, then return it. Note this performs a pre-increment.

On success returns the code point value. If `pos` was out of bounds (e.g. past the end of the string), return -1. On an error, such as an invalid byte sequence, return -2. As with al_ustr_prev, invalid byte sequences may be skipped while advancing.

See also: al_ustr_get_next

Examples:

- ex_utf8.c

# Inserting into strings

## al_ustr_insert

    bool al_ustr_insert(ALLEGRO_USTR *us1, int pos, const ALLEGRO_USTR *us2)

Source Code

Insert `us2` into `us1` beginning at byte offset `pos`. `pos` cannot be less than 0. If `pos` is past the end of `us1` then the space between the end of the string and `pos` will be padded with NUL (`'\0'`) bytes.

If required, use al_ustr_offset to find the byte offset for a given code point index.

Returns true on success, false on error.

See also: al_ustr_insert_cstr, al_ustr_insert_chr, al_ustr_append, al_ustr_offset

Examples:

- nihgui.cpp
- ex_utf8.c

## al_ustr_insert_cstr

    bool al_ustr_insert_cstr(ALLEGRO_USTR *us, int pos, const char *s)

Source Code

Like al_ustr_insert but inserts a C-style string at byte offset `pos`.

See also: al_ustr_insert, al_ustr_insert_chr

Examples:

- ex_utf8.c

## al_ustr_insert_chr

    size_t al_ustr_insert_chr(ALLEGRO_USTR *us, int pos, int32_t c)

Source Code

Insert a code point into `us` beginning at byte offset `pos`. `pos` cannot be less than 0. If `pos` is past the end of `us` then the space between the end of the string and `pos` will be padded with NUL (`'\0'`) bytes.

Returns the number of bytes inserted, or 0 on error.

See also: al_ustr_insert, al_ustr_insert_cstr

Examples:

- nihgui.cpp
- ex_utf8.c

# Appending to strings

## al_ustr_append

    bool al_ustr_append(ALLEGRO_USTR *us1, const ALLEGRO_USTR *us2)

Source Code

Append `us2` to the end of `us1`.

Returns true on success, false on error.

This function can be used to append an arbitrary buffer:

      ALLEGRO_USTR_INFO info;
      al_ustr_append(us, al_ref_buffer(&info, buf, size));

See also: al_ustr_append_cstr, al_ustr_append_chr, al_ustr_appendf, al_ustr_vappendf

Examples:

- ex_loading_thread.c
- ex_utf8.c

## al_ustr_append_cstr

    bool al_ustr_append_cstr(ALLEGRO_USTR *us, const char *s)

Source Code

Append C-style string `s` to the end of `us`.

Returns true on success, false on error.

See also: al_ustr_append

Examples:

- ex_loading_thread.c
- ex_utf8.c

## al_ustr_append_chr

    size_t al_ustr_append_chr(ALLEGRO_USTR *us, int32_t c)

Source Code

Append a code point to the end of `us`.

Returns the number of bytes added, or 0 on error.

See also: al_ustr_append

Examples:

- ex_utf8.c

## al_ustr_appendf

    bool al_ustr_appendf(ALLEGRO_USTR *us, const char *fmt, ...)

Source Code

This function appends formatted output to the string `us`. `fmt` is a printf-style format string. See al_ustr_newf about the “%s” and “%c” specifiers.

Returns true on success, false on error.

See also: al_ustr_vappendf, al_ustr_append

Examples:

- ex_utf8.c

## al_ustr_vappendf

    bool al_ustr_vappendf(ALLEGRO_USTR *us, const char *fmt, va_list ap)

Source Code

Like al_ustr_appendf but you pass the variable argument list directly, instead of the arguments themselves. See al_ustr_newf about the “%s” and “%c” specifiers.

Returns true on success, false on error.

See also: al_ustr_appendf, al_ustr_append

Examples:

- ex_utf8.c

# Removing parts of strings

## al_ustr_remove_chr

    bool al_ustr_remove_chr(ALLEGRO_USTR *us, int pos)

Source Code

Remove the code point beginning at byte offset `pos`. Returns true on success. If `pos` is out of range or `pos` is not the beginning of a valid code point, returns false leaving the string unmodified.

Use al_ustr_offset to find the byte offset for a code-points offset.

See also: al_ustr_remove_range

Examples:

- nihgui.cpp
- ex_utf8.c
- ex_logo.c

## al_ustr_remove_range

    bool al_ustr_remove_range(ALLEGRO_USTR *us, int start_pos, int end_pos)

Source Code

Remove the interval [`start_pos`, `end_pos`) from a string. `start_pos` and `end_pos` are byte offsets. Both may be past the end of the string but cannot be less than 0 (the start of the string).

Returns true on success, false on error.

See also: al_ustr_remove_chr, al_ustr_truncate

Examples:

- ex_utf8.c

## al_ustr_truncate

    bool al_ustr_truncate(ALLEGRO_USTR *us, int start_pos)

Source Code

Truncate a portion of a string from byte offset `start_pos` onwards. `start_pos` can be past the end of the string (has no effect) but cannot be less than 0.

Returns true on success, false on error.

See also: al_ustr_remove_range, al_ustr_ltrim_ws, al_ustr_rtrim_ws, al_ustr_trim_ws

Examples:

- ex_utf8.c

## al_ustr_ltrim_ws

    bool al_ustr_ltrim_ws(ALLEGRO_USTR *us)

Source Code

Remove leading whitespace characters from a string, as defined by the C function `isspace()`.

Returns true on success, or false on error.

See also: al_ustr_rtrim_ws, al_ustr_trim_ws

Examples:

- ex_utf8.c

## al_ustr_rtrim_ws

    bool al_ustr_rtrim_ws(ALLEGRO_USTR *us)

Source Code

Remove trailing (“right”) whitespace characters from a string, as defined by the C function `isspace()`.

Returns true on success, or false on error.

See also: al_ustr_ltrim_ws, al_ustr_trim_ws

Examples:

- ex_utf8.c

## al_ustr_trim_ws

    bool al_ustr_trim_ws(ALLEGRO_USTR *us)

Source Code

Remove both leading and trailing whitespace characters from a string.

Returns true on success, or false on error.

See also: al_ustr_ltrim_ws, al_ustr_rtrim_ws

Examples:

- ex_loading_thread.c
- ex_utf8.c

# Assigning one string to another

## al_ustr_assign

    bool al_ustr_assign(ALLEGRO_USTR *us1, const ALLEGRO_USTR *us2)

Source Code

Overwrite the string `us1` with another string `us2`. Returns true on success, false on error.

See also: al_ustr_assign_substr, al_ustr_assign_cstr

Examples:

- ex_utf8.c

## al_ustr_assign_substr

    bool al_ustr_assign_substr(ALLEGRO_USTR *us1, const ALLEGRO_USTR *us2,
       int start_pos, int end_pos)

Source Code

Overwrite the string `us1` with the contents of `us2` in the byte interval [`start_pos`, `end_pos`). The end points will be clamped to the bounds of `us2`.

Usually you will first have to use al_ustr_offset to find the byte offsets.

Returns true on success, false on error.

See also: al_ustr_assign, al_ustr_assign_cstr

Examples:

- ex_utf8.c

## al_ustr_assign_cstr

    bool al_ustr_assign_cstr(ALLEGRO_USTR *us1, const char *s)

Source Code

Overwrite the string `us1` with the contents of the C-style string `s`. Returns true on success, false on error.

See also: al_ustr_assign_substr, al_ustr_assign_cstr

Examples:

- ex_utf8.c

# Replacing parts of string

## al_ustr_set_chr

    size_t al_ustr_set_chr(ALLEGRO_USTR *us, int start_pos, int32_t c)

Source Code

Replace the code point beginning at byte offset `start_pos` with `c`. `start_pos` cannot be less than 0. If `start_pos` is past the end of `us` then the space between the end of the string and `start_pos` will be padded with NUL (`'\0'`) bytes. If `start_pos` is not the start of a valid code point, that is an error and the string will be unmodified.

On success, returns the number of bytes written, i.e. the offset to the following code point. On error, returns 0.

See also: al_ustr_replace_range

Examples:

- ex_utf8.c
- ex_logo.c

## al_ustr_replace_range

    bool al_ustr_replace_range(ALLEGRO_USTR *us1, int start_pos1, int end_pos1,
       const ALLEGRO_USTR *us2)

Source Code

Replace the part of `us1` in the byte interval [`start_pos1`, `end_pos1`) with the contents of `us2`. `start_pos1` cannot be less than 0. If `start_pos1` is past the end of `us1` then the space between the end of the string and `start_pos1` will be padded with NUL (`'\0'`) bytes.

Use al_ustr_offset to find the byte offsets.

Returns true on success, false on error.

See also: al_ustr_set_chr

Examples:

- ex_utf8.c

# Searching

## al_ustr_find_chr

    int al_ustr_find_chr(const ALLEGRO_USTR *us, int start_pos, int32_t c)

Source Code

Search for the encoding of code point `c` in `us` from byte offset `start_pos` (inclusive).

Returns the position where it is found or -1 if it is not found.

See also: al_ustr_rfind_chr

Examples:

- ex_utf8.c

## al_ustr_rfind_chr

    int al_ustr_rfind_chr(const ALLEGRO_USTR *us, int end_pos, int32_t c)

Source Code

Search for the encoding of code point `c` in `us` backwards from byte offset `end_pos` (exclusive). Returns the position where it is found or -1 if it is not found.

See also: al_ustr_find_chr

Examples:

- ex_utf8.c

## al_ustr_find_set

    int al_ustr_find_set(const ALLEGRO_USTR *us, int start_pos,
       const ALLEGRO_USTR *accept)

Source Code

This function finds the first code point in `us`, beginning from byte offset `start_pos`, that matches any code point in `accept`. Returns the position if a code point was found. Otherwise returns -1.

See also: al_ustr_find_set_cstr, al_ustr_find_cset

Examples:

- ex_utf8.c

## al_ustr_find_set_cstr

    int al_ustr_find_set_cstr(const ALLEGRO_USTR *us, int start_pos,
       const char *accept)

Source Code

Like al_ustr_find_set but takes a C-style string for `accept`.

See also: al_ustr_find_set, al_ustr_find_cset_cstr

Examples:

- ex_utf8.c

## al_ustr_find_cset

    int al_ustr_find_cset(const ALLEGRO_USTR *us, int start_pos,
       const ALLEGRO_USTR *reject)

Source Code

This function finds the first code point in `us`, beginning from byte offset `start_pos`, that does not match any code point in `reject`. In other words it finds a code point in the complementary set of `reject`. Returns the byte position of that code point, if any. Otherwise returns -1.

See also: al_ustr_find_cset_cstr, al_ustr_find_set

Examples:

- ex_utf8.c

## al_ustr_find_cset_cstr

    int al_ustr_find_cset_cstr(const ALLEGRO_USTR *us, int start_pos,
       const char *reject)

Source Code

Like al_ustr_find_cset but takes a C-style string for `reject`.

See also: al_ustr_find_cset, al_ustr_find_set_cstr

Examples:

- ex_utf8.c

## al_ustr_find_str

    int al_ustr_find_str(const ALLEGRO_USTR *haystack, int start_pos,
       const ALLEGRO_USTR *needle)

Source Code

Find the first occurrence of string `needle` in `haystack`, beginning from byte offset `start_pos` (inclusive). Return the byte offset of the occurrence if it is found, otherwise return -1.

See also: al_ustr_find_cstr, al_ustr_rfind_str, al_ustr_find_replace

Examples:

- ex_utf8.c

## al_ustr_find_cstr

    int al_ustr_find_cstr(const ALLEGRO_USTR *haystack, int start_pos,
       const char *needle)

Source Code

Like al_ustr_find_str but takes a C-style string for `needle`.

See also: al_ustr_find_str, al_ustr_rfind_cstr

Examples:

- ex_utf8.c

## al_ustr_rfind_str

    int al_ustr_rfind_str(const ALLEGRO_USTR *haystack, int end_pos,
       const ALLEGRO_USTR *needle)

Source Code

Find the last occurrence of string `needle` in `haystack` before byte offset `end_pos` (exclusive). Return the byte offset of the occurrence if it is found, otherwise return -1.

See also: al_ustr_rfind_cstr, al_ustr_find_str

Examples:

- ex_utf8.c

## al_ustr_rfind_cstr

    int al_ustr_rfind_cstr(const ALLEGRO_USTR *haystack, int end_pos,
       const char *needle)

Source Code

Like al_ustr_rfind_str but takes a C-style string for `needle`.

See also: al_ustr_rfind_str, al_ustr_find_cstr

Examples:

- ex_utf8.c

## al_ustr_find_replace

    bool al_ustr_find_replace(ALLEGRO_USTR *us, int start_pos,
       const ALLEGRO_USTR *find, const ALLEGRO_USTR *replace)

Source Code

Replace all occurrences of `find` in `us` with `replace`, beginning at byte offset `start_pos`. The `find` string must be non-empty. Returns true on success, false on error.

See also: al_ustr_find_replace_cstr

Examples:

- ex_loading_thread.c
- ex_utf8.c

## al_ustr_find_replace_cstr

    bool al_ustr_find_replace_cstr(ALLEGRO_USTR *us, int start_pos,
       const char *find, const char *replace)

Source Code

Like al_ustr_find_replace but takes C-style strings for `find` and `replace`.

Examples:

- ex_loading_thread.c
- ex_utf8.c

# Comparing

## al_ustr_equal

    bool al_ustr_equal(const ALLEGRO_USTR *us1, const ALLEGRO_USTR *us2)

Source Code

Return true iff the two strings are equal. This function is more efficient than al_ustr_compare so is preferable if ordering is not important.

See also: al_ustr_compare

Examples:

- ex_utf8.c

## al_ustr_compare

    int al_ustr_compare(const ALLEGRO_USTR *us1, const ALLEGRO_USTR *us2)

Source Code

This function compares `us1` and `us2` by code point values. Returns zero if the strings are equal, a positive number if `us1` comes after `us2`, else a negative number.

This does not take into account locale-specific sorting rules. For that you will need to use another library.

See also: al_ustr_ncompare, al_ustr_equal

Examples:

- ex_utf8.c

## al_ustr_ncompare

    int al_ustr_ncompare(const ALLEGRO_USTR *us1, const ALLEGRO_USTR *us2, int n)

Source Code

Like al_ustr_compare but only compares up to the first `n` code points of both strings.

Returns zero if the strings are equal, a positive number if `us1` comes after `us2`, else a negative number.

See also: al_ustr_compare, al_ustr_equal

Examples:

- ex_utf8.c

## al_ustr_has_prefix

    bool al_ustr_has_prefix(const ALLEGRO_USTR *us1, const ALLEGRO_USTR *us2)

Source Code

Returns true iff `us1` begins with `us2`.

See also: al_ustr_has_prefix_cstr, al_ustr_has_suffix

Examples:

- ex_utf8.c

## al_ustr_has_prefix_cstr

    bool al_ustr_has_prefix_cstr(const ALLEGRO_USTR *us1, const char *s2)

Source Code

Returns true iff `us1` begins with `s2`.

See also: al_ustr_has_prefix, al_ustr_has_suffix_cstr

Examples:

- ex_utf8.c

## al_ustr_has_suffix

    bool al_ustr_has_suffix(const ALLEGRO_USTR *us1, const ALLEGRO_USTR *us2)

Source Code

Returns true iff `us1` ends with `us2`.

See also: al_ustr_has_suffix_cstr, al_ustr_has_prefix

Examples:

- ex_utf8.c

## al_ustr_has_suffix_cstr

    bool al_ustr_has_suffix_cstr(const ALLEGRO_USTR *us1, const char *s2)

Source Code

Returns true iff `us1` ends with `s2`.

See also: al_ustr_has_suffix, al_ustr_has_prefix_cstr

Examples:

- ex_utf8.c

# UTF-16 conversion

## al_ustr_new_from_utf16

    ALLEGRO_USTR *al_ustr_new_from_utf16(uint16_t const *s)

Source Code

Create a new string containing a copy of the 0-terminated string `s` which must be encoded as UTF-16. The string must eventually be freed with al_ustr_free.

See also: al_ustr_new

Examples:

- ex_utf8.c

## al_ustr_size_utf16

    size_t al_ustr_size_utf16(const ALLEGRO_USTR *us)

Source Code

Returns the number of bytes required to encode the string in UTF-16 (including the terminating 0). Usually called before al_ustr_encode_utf16 to determine the size of the buffer to allocate.

See also: al_ustr_size

Examples:

- ex_utf8.c

## al_ustr_encode_utf16

    size_t al_ustr_encode_utf16(const ALLEGRO_USTR *us, uint16_t *s,
       size_t n)

Source Code

Encode the string into the given buffer, in UTF-16. Returns the number of bytes written. There are never more than `n` bytes written. The minimum size to encode the complete string can be queried with al_ustr_size_utf16. If the `n` parameter is smaller than that, the string will be truncated but still always 0 terminated.

See also: al_ustr_size_utf16, al_utf16_encode

Examples:

- ex_utf8.c

# Low-level UTF-8 routines

## al_utf8_width

    size_t al_utf8_width(int32_t c)

Source Code

Returns the number of bytes that would be occupied by the specified code point when encoded in UTF-8. This is between 1 and 4 bytes for legal code point values. Otherwise returns 0.

See also: al_utf8_encode, al_utf16_width

Examples:

- nihgui.cpp
- ex_utf8.c

## al_utf8_encode

    size_t al_utf8_encode(char s[], int32_t c)

Source Code

Encode the specified code point to UTF-8 into the buffer `s`. The buffer must have enough space to hold the encoding, which takes between 1 and 4 bytes. This routine will refuse to encode code points above 0x10FFFF.

Returns the number of bytes written, which is the same as that returned by al_utf8_width.

See also: al_utf16_encode

Examples:

- ex_keyboard_events.c
- ex_utf8.c

# Low-level UTF-16 routines

## al_utf16_width

    size_t al_utf16_width(int c)

Source Code

Returns the number of bytes that would be occupied by the specified code point when encoded in UTF-16. This is either 2 or 4 bytes for legal code point values. Otherwise returns 0.

See also: al_utf16_encode, al_utf8_width

## al_utf16_encode

    size_t al_utf16_encode(uint16_t s[], int32_t c)

Source Code

Encode the specified code point to UTF-16 into the buffer `s`. The buffer must have enough space to hold the encoding, which takes either 2 or 4 bytes. This routine will refuse to encode code points above 0x10FFFF.

Returns the number of bytes written, which is the same as that returned by al_utf16_width.

See also: al_utf8_encode, al_ustr_encode_utf16

Allegro version 5.2.11 - Last updated: 2026-02-09 02:00:42 UTC