strbuf’s are meant to be used with all the usual C string and memory APIs. Given that the length of the buffer is known, it’s often better to use the mem* functions than a str* one (memchr vs. strchr e.g.). Though, one has to be careful about the fact that str* functions often stop on NULs and that strbufs may have embedded NULs.

An strbuf is NUL terminated for convenience, but no function in the strbuf API actually relies on the string being free of NULs.

strbufs has some invariants that are very important to keep in mind:

  1. The buf member is never NULL, so it can be used in any usual C string operations safely. strbuf’s have to be initialized either by strbuf_init() or by = STRBUF_INIT before the invariants, though.

    Do not assume anything on what buf really is (e.g. if it is allocated memory or not), use strbuf_detach() to unwrap a memory buffer from its strbuf shell in a safe way. That is the sole supported way. This will give you a malloced buffer that you can later free().

    However, it is totally safe to modify anything in the string pointed by the buf member, between the indices 0 and len-1 (inclusive).

  2. The buf member is a byte array that has at least len + 1 bytes allocated. The extra byte is used to store a '\0', allowing the buf member to be a valid C-string. Every strbuf function ensure this invariant is preserved.

    Note
    		 It is OK to "play" with the buffer directly if you work it this way: 
    strbuf_grow(sb, SOME_SIZE); <1>
strbuf_setlen(sb, sb->len + SOME_OTHER_SIZE);

    1. Here, the memory array starting at sb->buf, and of length strbuf_avail(sb) is all yours, and you can be sure that strbuf_avail(sb) is at least SOME_SIZE.

      Note
      		 SOME_OTHER_SIZE must be smaller or equal to strbuf_avail(sb).

      Doing so is safe, though if it has to be done in many places, adding the missing API to the strbuf module is the way to go.

      Warning
      		 Do not assume that the area that is yours is of size alloc - 1 even if it’s true in the current implementation. Alloc is somehow a "private" member that should not be messed with. Use strbuf_avail() instead.

Data structures

  • struct strbuf

This is the string buffer structure. The len member can be used to determine the current length of the string, and buf member provides access to the string itself.

Functions

  • Life cycle

    strbuf_init

    Initialize the structure. The second parameter can be zero or a bigger number to allocate memory, in case you want to prevent further reallocs.

    strbuf_release

    Release a string buffer and the memory it used. You should not use the string buffer after using this function, unless you initialize it again.

    strbuf_detach

    Detach the string from the strbuf and returns it; you now own the storage the string occupies and it is your responsibility from then on to release it with free(3) when you are done with it.

    strbuf_attach

    Attach a string to a buffer. You should specify the string to attach, the current length of the string and the amount of allocated memory. The amount must be larger than the string length, because the string you pass is supposed to be a NUL-terminated string. This string must be malloc()ed, and after attaching, the pointer cannot be relied upon anymore, and neither be free()d directly.

    strbuf_swap

    Swap the contents of two string buffers.

  • Related to the size of the buffer

    strbuf_avail

    Determine the amount of allocated but unused memory.

    strbuf_grow

    Ensure that at least this amount of unused memory is available after len. This is used when you know a typical size for what you will add and want to avoid repetitive automatic resizing of the underlying buffer. This is never a needed operation, but can be critical for performance in some cases.

    strbuf_setlen

    Set the length of the buffer to a given value. This function does not allocate new memory, so you should not perform a strbuf_setlen() to a length that is larger than len + strbuf_avail(). strbuf_setlen() is just meant as a please fix invariants from this strbuf I just messed with.

    strbuf_reset

    Empty the buffer by setting the size of it to zero.

  • Related to the contents of the buffer

    strbuf_rtrim

    Strip whitespace from the end of a string.

    strbuf_cmp

    Compare two buffers. Returns an integer less than, equal to, or greater than zero if the first buffer is found, respectively, to be less than, to match, or be greater than the second buffer.

  • Adding data to the buffer

Note
 All of the functions in this section will grow the buffer as necessary. If they fail for some reason other than memory shortage and the buffer hadn’t been allocated before (i.e. the struct strbuf was set to STRBUF_INIT), then they will free() it.
strbuf_addch

Add a single character to the buffer.

strbuf_insert

Insert data to the given position of the buffer. The remaining contents will be shifted, not overwritten.

strbuf_remove

Remove given amount of data from a given position of the buffer.

strbuf_splice

Remove the bytes between pos..pos+len and replace it with the given data.

strbuf_add

Add data of given length to the buffer.

strbuf_addstr

Add a NUL-terminated string to the buffer.

Note
 This function will always be implemented as an inline or a macro that expands to: 
strbuf_add(..., s, strlen(s));

Meaning that this is efficient to write things like:

strbuf_addstr(sb, "immediate string");
strbuf_addbuf

Copy the contents of an other buffer at the end of the current one.

strbuf_adddup

Copy part of the buffer from a given position till a given length to the end of the buffer.

strbuf_expand

This function can be used to expand a format string containing placeholders. To that end, it parses the string and calls the specified function for every percent sign found.

The callback function is given a pointer to the character after the % and a pointer to the struct strbuf. It is expected to add the expanded version of the placeholder to the strbuf, e.g. to add a newline character if the letter n appears after a %. The function returns the length of the placeholder recognized and strbuf_expand() skips over it.

The format %% is automatically expanded to a single % as a quoting mechanism; callers do not need to handle the % placeholder themselves, and the callback function will not be invoked for this placeholder.

All other characters (non-percent and not skipped ones) are copied verbatim to the strbuf. If the callback returned zero, meaning that the placeholder is unknown, then the percent sign is copied, too.

In order to facilitate caching and to make it possible to give parameters to the callback, strbuf_expand() passes a context pointer, which can be used by the programmer of the callback as she sees fit.

strbuf_expand_dict_cb

Used as callback for strbuf_expand(), expects an array of struct strbuf_expand_dict_entry as context, i.e. pairs of placeholder and replacement string. The array needs to be terminated by an entry with placeholder set to NULL.

strbuf_addbuf_percentquote

Append the contents of one strbuf to another, quoting any percent signs ("%") into double-percents ("%%") in the destination. This is useful for literal data to be fed to either strbuf_expand or to the *printf family of functions.

strbuf_addf

Add a formatted string to the buffer.

strbuf_fread

Read a given size of data from a FILE* pointer to the buffer.

Note
 The buffer is rewound if the read fails. If -1 is returned, errno must be consulted, like you would do for read(3). strbuf_read(), strbuf_read_file() and strbuf_getline() has the same behaviour as well.
strbuf_read

Read the contents of a given file descriptor. The third argument can be used to give a hint about the file size, to avoid reallocs.

strbuf_read_file

Read the contents of a file, specified by its path. The third argument can be used to give a hint about the file size, to avoid reallocs.

strbuf_readlink

Read the target of a symbolic link, specified by its path. The third argument can be used to give a hint about the size, to avoid reallocs.

strbuf_getline

Read a line from a FILE *, overwriting the existing contents of the strbuf. The second argument specifies the line terminator character, typically '\n'. Reading stops after the terminator or at EOF. The terminator is removed from the buffer before returning. Returns 0 unless there was nothing left before EOF, in which case it returns EOF.

strbuf_getwholeline

Like strbuf_getline, but keeps the trailing terminator (if any) in the buffer.

strbuf_getwholeline_fd

Like strbuf_getwholeline, but operates on a file descriptor. It reads one character at a time, so it is very slow. Do not use it unless you need the correct position in the file descriptor.

stripspace

Strip whitespace from a buffer. The second parameter controls if comments are considered contents to be removed or not.

launch_editor

Launch the user preferred editor to edit a file and fill the buffer with the file’s contents upon the user completing their editing. The third argument can be used to set the environment which the editor is run in. If the buffer is NULL the editor is launched as usual but the file’s contents are not read into the buffer upon completion.