Function rcutils_repl_str

Function Documentation

char *rcutils_repl_str(const char *str, const char *from, const char *to, const rcutils_allocator_t *allocator)

Replace all the occurrences of one string for another in the given string.

Documentation copied from the source with minor tweaks:

Description:

Replaces in the string str all the occurrences of the source string from with the destination string to. The lengths of the strings from and to may differ. The string to may be of any length, but the string from must be of non-zero length - the penalty for providing an empty string for the from parameter is an infinite loop. In addition, none of the three parameters may be NULL.

Returns:

The post-replacement string, or NULL if memory for the new string could not be allocated. Does not modify the original string. The memory for the returned post-replacement string may be deallocated with given allocator’s deallocate function when it is no longer required.

Performance:

In case you are curious enough to want to compare this implementation with alternative implementations, you are welcome to compile and run the code in the benchmarking file, replacebench.c. In that file, the above function is included as replace_cache, and the functions originally published on this page as replace_str2 and replace_str are included as replace_opt2 and replace_opt. Code/functions are included from the comp.lang.c thread, how to replace a substring in a string using C?, from answers to the stackoverflow question, What is the function to replace string in C?, and also from private correspondence. See the comments top of file for instructions on compiling and running it.

In most scenarios, the fastest replacement function, by around 10-20%, is Albert Chan’s replace_smart, followed by the above function: repl_str aka replace_cache. There are some scenarios, though, where repl_str is faster than replace_smart, sometimes by up to 200%. These scenarios involve long strings with few matches. Why, if Albert’s function is generally slightly faster than the above repl_str function, is it not the focus of this page? Because it generally uses much more memory than repl_str.

The third fastest implementation is typically replace_str2 aka replace_opt2. For longer strings in the case in which the lengths of the “from” and “to” strings differ, repl_str aka replace_cache beats it by margins of up to about 80%. For smaller strings, and in the case where the lengths of the “from” and “to” strings are identical, replace_str2 aka replace_opt2 is faster, by a maximum margin of about 35%, sometimes in those scenarios beating replace_smart too. Some of the other functions are also faster for smaller strings. The even-match point between replace_str2 and repl_str (assuming “from” and “to” string lengths differ) depends on how far into the string the final match occurs, how many matches there are, and the comparative lengths of the old and “to” strings, but roughly it occurs for strings of 700-800 bytes in length.

This analysis is based on compiling with GCC and testing on a 64-bit Intel platform running Linux, however brief testing with Microsoft Visual C++ 2010 Express (scroll down to “Additional information” at that link) on Windows 7 seemed to produce similar results.

Here continues additional documentation added by OSRF.

The allocator must not be NULL.

Parameters:

  • str – [in] string to have substrings found and replaced within

  • from – [in] string to match for replacement

  • to – [in] string to replace matched strings with

  • allocator – [in] structure defining functions to be used for allocation

Returns:

duplicated str with all matches of from replaced with to.