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Edit File: Design.Strings.txt

Dynamic Strings
===============

'lib/str.h' describes Dovecot's dynamically growing strings. Strings are
actually only a simple wrapper on top of <buffers> [Design.Buffers.txt]. Even
the 'string_t' type is only a typedef of 'buffer_t', so it's possible to use
'buffer_*()' functions with strings (although it's ugly so it should be
avoided). The decision of whether to use a string_t or a buffer_t is mainly for
human readability: if the buffer's contents are (ASCII/UTF8) text use string_t,
otherwise for binary data use buffer_t.

Once you're done modifying a string with 'str_*()' functions, you can get it
out as a NUL-terminated string with 'str_c()' or 'str_c_modifiable()'. These
pointers shouldn't be accessed after modifying the string again, they could
have moved elsewhere in memory and they're no longer guaranteed to be
NUL-terminated.

Example:

---%<-------------------------------------------------------------------------
T_BEGIN {
  string_t *str = t_str_new(64);

str_append(str, "hello world");
  str_printfa(str, "\nand %u", str_len(str));

printf("%s\n", str_c(str));
} T_END;
---%<-------------------------------------------------------------------------

String Handling Functions
=========================

'lib/strfuncs.h' contains a lot of functions intended to make string handling
easier. They use C's NUL-terminated strings instead of Dovecot's dynamic
strings.

* '[pt]_strdup_printf()' and '[pt]_strconcat()' are the most commonly used
   functions.'*_strconcat' is slightly faster than '*_strdup_printf()', so use
   it if you simply need to concatenate strings.
 * Various functions for doing a 'strdup()' from wanted input.
 * 'i_snprintf()' is a wrapper to 'snprintf()' that makes it easier to check if
   result was truncated. It also adds few other safety checks. This should be
   avoided in general, except in situations where you just don't want to use
   data stack and there's no way for the result to get truncated.
 * 'i_strocpy()' is similar to 'strlcpy()', but makes it easier to check if
   result was truncated. This has the same problems as 'i_snprintf()'.
 * Functions for uppercasing and lowercasing strings.
 * Functions you can pass to 'bsearch()' and 'qsort()' for handling string
   arrays.
 * '[pt]_strsplit()' is an easy way to split a string into an array of strings
   from given separator.
    * 't_strarray_join()' reverses this.
    * There are also some other functions to handle array of strings, like
      getting its length or finding a given string.
 * 'dec2str()' can be used to convert a number to a string. This can be useful
   if you don't know the correct type and don't want to add casting (that could
   potentially truncate the string). For example:'print("pid = %s\n",
   dec2str(getpid()));'

String Escaping
===============

'lib/strescape.h' contains functions to escape and unescape <">. <'> and <\>
characters in strings using<\> character.\

Dovecot's internal protocols are often line-based with TAB as the field
separator. This file also contains functions to escape and unescape such data.

(This file was created from the wiki on 2018-05-23 04:42)