FindString Example in C

findstring_demo.c

#include <stdio.h>
#include <string.h>
#include <stdint.h>
#include <ctype.h>

#define MATCH_NOT_FOUND SIZE_MAX

size_t findstring(const char* str, const char* match, size_t current_pos);

void main(void)
{
	const char* redact_words[] = { "hello", "world" };
	const int num_redact_words = 2;
	char test_string[] = "Hello world in the world we call home and say hello!";

	printf("Current test string: '%s'\n", test_string);

	for (int i = 0; i < num_redact_words; i++) {

		const char* match = redact_words[i];
		size_t found_pos = MATCH_NOT_FOUND;

		while ((found_pos = findstring(test_string, match, found_pos + 1, 0)) != MATCH_NOT_FOUND)
		{
			printf("Found at position: %I64d\n", found_pos);

			memset(test_string + found_pos, '*', strlen(match));
		}
	}

	printf("Changed test string: '%s'", test_string);

	printf("\n");
}

size_t findstring(const char* str, const char* match, size_t pos, int ignore_case)
{
	size_t match_pos = 0;
	size_t match_len = strlen(match);
	size_t start_match = MATCH_NOT_FOUND;

	while (str[pos]) 
	{
		if ((!ignore_case && str[pos] == match[match_pos]) ||
			(ignore_case && tolower(str[pos]) == tolower(match[match_pos])))
		{
			// In a potential match:
			if (start_match == MATCH_NOT_FOUND) start_match = pos;
			match_pos++;
		}
		else
		{
			// Reset
			start_match = MATCH_NOT_FOUND;
			match_pos = 0;
		}

		if (match_pos == match_len)
		{
			// Found full match, we're done
			break;
		}

		pos++;
	}

	return start_match;
}