Thread: C & Regular Expressions

Hi, so I'm new to this site.


I just posted a post it and already has more than 4 thousand views!


I have a question.


I am not well versed with PCRE2.



In my other thread, the attached file had a gsub() function that takes three arguments.

Code:

#define PCRE2_CODE_UNIT_WIDTH 8
#include <pcre2.h>




char* gsub  (const char* str, const char*     reg, const char* rep) {
size_t outlen;
    static const char* error_str = \"DONT KNOW HOW TO ALLOCATE MEM FOR REGEX\";
    char* out = malloc(outlen =strlen(str) *      strlen(rep))  ;
    if (out == NULL) {
        error:
    fputs(error_str,   stderr);
return NULL;
    }


    
    int error;
    PCRE2_SIZE erroffset;
//                                       printf(\"       %l                             \", 
    const PCRE2_SPTR pattern = (PCRE2_SPTR)reg;
    const PCRE2_SPTR subject = (PCRE2_SPTR)str;
    const PCRE2_SPTR replacement = (PCRE2_SPTR)rep;


    pcre2_code *re = pcre2_compile(pattern, PCRE2_ZERO_TERMINATED, 0, &error, &erroffset, 0);
    if (re == 0) return NULL;
//        return 1;


    pcre2_jit_compile(re, PCRE2_JIT_COMPLETE);


    int rc = pcre2_substitute(re, subject, PCRE2_ZERO_TERMINATED, 0, PCRE2_SUBSTITUTE_GLOBAL | PCRE2_SUBSTITUTE_EXTENDED, 0, 0, replacement, PCRE2_ZERO_TERMINATED, out, &outlen);
    if (rc >= 0);
//        printf(%s\\n, output);


    pcre2_code_free(re);
    size_t new_len = strlen(out);
    char* new_out = realloc(out,new_len + 1);
    if (new_out == NULL) goto error;




    return   new_out;
   }

The PCRE2 API is really complicated.



Questions

1. Is there any way to have PCRE automatically account for memory allocation sizes? With a callback, I could do this manually.

2. So is the best solution to always have a callback function?


3. I want to implement something like Ruby's

str.gsub /foo/ do |i|
....
end


Could someone post a code snippet that does this?



4. Would anyone want to contribute to my other project? (https://cboard.cprogramming.com/c-programming/181160-hi-i-have-created-some-work-i-think-will-really-valuable-community.html)



I can re-write it in C.


It's just the current compiler is using gsub() functions in Crystal.


I'm not an expert in PCRE2.


Thank you.