Question

How to match words in a string that are wrapped in curly brackets using RegEx with C

Answer 1

#include <stdio.h>
#include <regex.h>
#include <string.h>

int main() {
    const char *text = "This is a {string} with {words} in curly {brackets}";
    const char *pattern = "\\{([^}]+)\\}";
    regex_t regex;
    regmatch_t matches[2]; // To store the entire match and the capturing group
    int start = 0;

    // Compile the regular expression
    if (regcomp(&regex, pattern, REG_EXTENDED) != 0) {
        fprintf(stderr, "Could not compile regex\n");
        return 1;
    }

    while (start < strlen(text) &&
           regexec(&regex, text + start, 2, matches, 0) == 0) {
        // Extract the match
        int match_start = matches[1].rm_so + start; // Capturing group 1 start
        int match_end = matches[1].rm_eo + start;   // Capturing group 1 end

        // Print the content inside curly braces
        printf("Found: ");
        for (int i = match_start; i < match_end; i++) {
            putchar(text[i]);
        }
        printf("\n");

        // Move the start position to continue searching after this match
        start += matches[0].rm_eo;
    }

    // Free the compiled regex
    regfree(&regex);

    return 0;
}



/*
run:

Found: string
Found: words
Found: brackets

*/

 

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Answer 2

#include <stdio.h>
#include <stdlib.h>
#include <regex.h>
#include <string.h>

// Function to find and return all content within curly braces
char** findCurlyBracesContent(const char* text, int* resultCount) {
    const char* pattern = "\\{([^}]+)\\}";
    regex_t regex;
    regmatch_t matches[2];
    char** results = NULL; // Dynamic array to store results
    *resultCount = 0;      // Initialize result count
    int start = 0;

    // Compile the regular expression
    if (regcomp(&regex, pattern, REG_EXTENDED) != 0) {
        fprintf(stderr, "Could not compile regex\n");
        return NULL;
    }

    // Search the input string for matches
    while (start < strlen(text) &&
           regexec(&regex, text + start, 2, matches, 0) == 0) {
        // Get start and end positions of the match
        int match_start = matches[1].rm_so + start; // Capturing group 1 start
        int match_end = matches[1].rm_eo + start;   // Capturing group 1 end
        int length = match_end - match_start;

        // Allocate memory for the new match
        char* match = (char*)malloc((length + 1) * sizeof(char));
        strncpy(match, text + match_start, length);
        match[length] = '\0'; 

        // Expand the results array and store the match
        results = (char**)realloc(results, (*resultCount + 1) * sizeof(char*));
        results[*resultCount] = match;
        (*resultCount)++;

        // Move the search start to the end of the current match
        start += matches[0].rm_eo;
    }

    // Free the compiled regex
    regfree(&regex);

    return results;
}

// Function to free memory allocated for the results
void freeResults(char** results, int count) {
    for (int i = 0; i < count; i++) {
        free(results[i]);
    }
    free(results);
}

int main() {
    const char* text = "This is a {string} with {words} in curly {brackets}";
    int resultCount = 0;

    char** results = findCurlyBracesContent(text, &resultCount);

    for (int i = 0; i < resultCount; i++) {
        printf("Found: %s\n", results[i]);
    }

    freeResults(results, resultCount);

    return 0;
}



/*
run:

Found: string
Found: words
Found: brackets

*/

 

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