使用regex.h在c中进行模式匹配/提取

Question

I need help extracting a substring from a string using regex.h in C. In this example, I am trying to extract all occurrences of character 'e' from a string 'telephone'. Unfortunately, I get stuck identifying the offsets of those characters. I am listing code below:

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

int main(void) {
    const int size=10;
    regex_t regex;
    regmatch_t matchStruct[size];

    char pattern[] = "(e)";
    char str[] = "telephone";

    int failure = regcomp(&regex, pattern, REG_EXTENDED);
    if (failure) {
        printf("Cannot compile");
    }

    int matchFailure = regexec(&regex, pattern, size, matchStruct, 0);
    if (!matchFailure) {
        printf("\nMatch!!");
    } else {
        printf("NO Match!!");
    }

    return 0;
}

So per GNU's manual, I should get all of the occurrences of 'e' when a character is parenthesized. However, I always get only the first occurrence.

Essentially, I want to be able to see something like:

matchStruct[1].rm_so = 1;
matchStruct[1].rm_so = 2;

matchStruct[2].rm_so = 4;
matchStruct[2].rm_so = 5;

matchStruct[3].rm_so = 7;
matchStruct[3].rm_so = 8;

or something along these lines. Any advice?

Answer 1

Please note that you are in fact not comparing your compiled regex against str ("telephone") but rather to your plain-text pattern . Check your second attribute to regexec . That fixed, proceed for instance to " regex in C language using functions regcomp and regexec toggles between first and second match " where the answer to your question is already given.