strseg - Get delimiter-separated segments from a string in a non-destructive method

example.c

#include <stdbool.h>
#include <stdio.h>
#include <stdlib.h>
#include "segstr.h"

int main(void) {
	char *string = "The Quick Brown Fox Jumped Over The Lazy Dog";

	char *segment = string;
	size_t segment_len;
	unsigned int segment_num = 0;
	while (true) {
		segment = segstr(segment, &segment_len, ' ', &segment_num);

		if (!segment) {
			puts("Printed all of the words in the sentence!");
			return EXIT_SUCCESS;
		}

		// Skip the word "The"
		if (segequstr(segment, segment_len, "The")) continue;

		printf("Word No. %u in sentence: %.*s\n", segment_num, (int) segment_len, segment);
	}
}

segstr.h

#include <stdbool.h>
#include <string.h>

/// @brief Get delimiter-separated segments from a string in a non-destructive method.
/// @details A useful function which can be used for parsing in a loop in a safe manner.
/// @author Damon Harris (TheDcoder@protonmail.com)
/// @param [in]     str        Current segment or start of the string.
/// @param [in,out] seg_len    Length of the current segment, value does not matter if `seg_num` is set to 0.
/// @param          delim      Character used for separation (delimiter).
/// @param [in,out] seg_num    Number of the current segment, set to 0 before first call.
/// @returns Pointer to the start of the next segment, `seg_len` is set to the length of the segment and `seg_num` is incremented by 1.
///          NULL if there is no next segment, note that NULL is never returned on the first call (even if an empty string is passed).
/// @remarks `seg_num` only has significance if its value is 0, the reason is for the function to be able to detect the initial call
///          so that it doesn't skip the first segment. `seg_len` can be any value on the first call since it is not used to calculate
///          the start of the next segment.
///
///          I was inspired by the lack of a helper function which I can use for parsing/tokenizing a string which is both stateless
///          and non-destructive (`strtok_s` is better than `strtok` but still modifies the supplied string). The best alternative was to
///          `strchr` and keep track of other stuff manually, this function tries to give out as much information as possible while keeping
///          the overall concept simple. The length and position (number) of the segment should be enough to get you started on parsing :)
char *segstr(const char *str, size_t *seg_len, char delim, unsigned int *seg_num) {
	if (*seg_num != 0) {
		// Check if we have reached the last segment
		str += *seg_len;
		if (str[0] == '\0') return NULL;

		// Proceed to the next segment
		++str;
	}

	// Increment the segment number
	++*seg_num;

	// Find the delimiter
	char *delim_start = strchr(str, delim);

	// Calculate the length of the segment
	if (delim_start) {
		// Difference between the delimiter and the start of the segment
		*seg_len = delim_start - str;
	} else {
		// We have reached the last segment
		// There is no delimiter, so use the remaining length
		*seg_len = strlen(str);
	}

	// Return the segment
	return (char *) str;
}

/// @brief Check a segment for equality with a string
/// @author Jan Alexander Steffens (jan.steffens@gmail.com)
/// @param seg        Segment to test for equality.
/// @param seg_len    Length of the segment.
/// @param str        String to match with the segment.
/// @returns `true` if `str` is equal to `seg`, otherwise `false`.
/// @remarks This function was made as a convenience alternative to `strncmp`.
///          I would like to thank heftig from the ##c IRC channel at freenode for coming up with the code based on my concept!
bool segequstr(char *seg, size_t seg_len, char *str) {
	return strncmp(seg, str, seg_len) == 0 && str[seg_len] == '\0';
}

UNLICENSE

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