somebodymodest/utf8.h

single header utf8 string functions for C and C++

utf8.h

A simple one header solution to supporting utf8 strings in C and C++.

Functions provided from the C header string.h but with a utf8* prefix instead of the str* prefix:

API function docs

string.h	utf8.h	complete
strcat	utf8cat	✔
strchr	utf8chr	✔
strcmp	utf8cmp	✔
strcoll	utf8coll
strcpy	utf8cpy	✔
strcspn	utf8cspn	✔
strdup	utf8dup	✔
strfry	utf8fry
strlen	utf8len	✔
strncat	utf8ncat	✔
strncmp	utf8ncmp	✔
strncpy	utf8ncpy	✔
strndup	utf8ndup	✔
strpbrk	utf8pbrk	✔
strrchr	utf8rchr	✔
strsep	utf8sep
strspn	utf8spn	✔
strstr	utf8str	✔
strtok	utf8tok
strxfrm	utf8xfrm

Functions provided from the C header strings.h but with a utf8* prefix instead of the str* prefix:

strings.h	utf8.h	complete
strcasecmp	utf8casecmp	✔
strncasecmp	utf8ncasecmp	✔
strcasestr	utf8casestr	✔

Functions provided that are unique to utf8.h:

utf8.h	complete
utf8codepoint	✔
utf8size	✔
utf8valid	✔
utf8codepointsize	✔
utf8catcodepoint	✔
utf8isupper
utf8islower
utf8lwr
utf8upr

Usage

Just include utf8.h in your code!

The current supported compilers are gcc, clang and msvc.

The current tested compiler versions are gcc 4.8.2, clang 3.5 and MSVC 18.0.21005.1.

Design

The utf8.h API matches the string.h API as much as possible by design. There are a few major differences though.

I use void* instead of char* when passing around utf8 strings. My reasoning is that I really don't want people accidentally thinking they can use integer arthimetic on the pointer and always get a valid character like you would with an ASCII string. Having it as a void* forces a user to explicitly cast the utf8 string to char* such that the onus is on them not to break the code anymore!

Anywhere in the string.h or strings.h documentation where it refers to 'bytes' I have changed that to utf8 codepoints. For instance, utf8len will return the number of utf8 codepoints in a utf8 string - which does not necessarily equate to the number of bytes.

API function docs

int utf8casecmp(const void *src1, const void *src2);

While ignoring the case of ASCII characters,
return less than 0, 0, greater than 0
if src1 < src2, src1 == src2, src1 > src2 respectively.

void *utf8cat(void *dst, const void *src);

Append the utf8 string src onto the utf8 string dst.

void *utf8chr(const void *src, long chr);

Find the first match of the utf8 codepoint chr in the utf8 string src.

int utf8cmp(const void *src1, const void *src2);

Return less than 0, 0, greater than 0 if src1 < src2,
src1 == src2, src1 > src2 respectively.

void *utf8cpy(void *dst, const void *src);

Copy the utf8 string src onto the memory allocated in dst.

size_t utf8cspn(const void *src, const void *reject);

Number of utf8 codepoints in the utf8 string src that consists entirely
of utf8 codepoints not from the utf8 string reject.

void *utf8dup(const void *src);

Duplicate the utf8 string src by getting its size, mallocing a new buffer
copying over the data, and returning that. Or 0 if malloc failed.

size_t utf8len(const void *str);

Number of utf8 codepoints in the utf8 string str,
excluding the null terminating byte.

int utf8ncasecmp(const void *src1, const void *src2, size_t n);

While ignoring the case of ASCII characters, return less
than 0, 0, greater than 0 if src1 < src2, src1 == src2,
src1 > src2 respectively. Checking at most n
bytes of each utf8 string.

void *utf8ncat(void *dst, const void *src, size_t n);

Append the utf8 string src onto the utf8 string dst,
writing at most n+1 bytes. Can produce an invalid utf8
string if n falls partway through a utf8 codepoint.

int utf8ncmp(const void *src1, const void *src2, size_t n);

Return less than 0, 0, greater than 0 if src1 < src2,
src1 == src2, src1 > src2 respectively. Checking at most n
bytes of each utf8 string.

void *utf8ncpy(void *dst, const void *src, size_t n);

Copy the utf8 string src onto the memory allocated in dst.
Copies at most n bytes. If there is no terminating null byte in
the first n bytes of src, the string placed into dst will not be
null-terminated. If the size (in bytes) of src is less than n,
extra null terminating bytes are appended to dst such that at
total of n bytes are written. Can produce an invalid utf8
string if n falls partway through a utf8 codepoint.

void *utf8pbrk(const void *str, const void *accept);

Locates the first occurence in the utf8 string str of any byte in the
utf8 string accept, or 0 if no match was found.

void *utf8rchr(const void *src, int chr);

Find the last match of the utf8 codepoint chr in the utf8 string src.

size_t utf8size(const void *str);

Number of bytes in the utf8 string str,
including the null terminating byte.

size_t utf8spn(const void *src, const void *accept);

Number of utf8 codepoints in the utf8 string src that consists entirely
of utf8 codepoints from the utf8 string accept.

void *utf8str(const void *haystack, const void *needle);

The position of the utf8 string needle in the utf8 string haystack.

void *utf8casestr(const void *haystack, const void *needle);

The position of the utf8 string needle in the utf8 string haystack, case instensitive.

void *utf8valid(const void *str);

Return 0 on success, or the position of the invalid utf8 codepoint on failure.

void *utf8codepoint(const void *str, long *out_codepoint);

Sets out_codepoint to the next utf8 codepoint in str,
and returns the address of the utf8 codepoint after the current one in str.

Todo

• Implement utf8coll (akin to strcoll).
• Implement utf8fry (akin to strfry).
• Add NULL pointer support. Should I NULL check the arguments to the API?
• Add Doxygen (or similar) to mimic the Unix man pages for string.h.
• Investigate adding dst buffer sizes for utf8cpy and utf8cat to catch overwrites (as suggested by @FlohOfWoe in https://twitter.com/FlohOfWoe/status/618669237771608064)
• Investigate adding a utf8canon which would turn 'bad' utf8 sequences (like ASCII values encoded in 4-byte utf8 codepoints) into their 'good' equivalents (as suggested by @KmBenzie)
• Investigate changing to Creative Commons Zero License (as suggested by @mcclure111)
• Add utf8casecmp and utf8ncasecmp to compare two strings case-insensitively (as insensitively suggested by @daniel_collin)
• Extend utf8casecmp range to consume non-ASCII case differences too (I don't even rightly know if there are any!)

License

This is free and unencumbered software released into the public domain.

Anyone is free to copy, modify, publish, use, compile, sell, or distribute this software, either in source code form or as a compiled binary, for any purpose, commercial or non-commercial, and by any means.

In jurisdictions that recognize copyright laws, the author or authors of this software dedicate any and all copyright interest in the software to the public domain. We make this dedication for the benefit of the public at large and to the detriment of our heirs and successors. We intend this dedication to be an overt act of relinquishment in perpetuity of all present and future rights to this software under copyright law.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

For more information, please refer to http://unlicense.org/