CCC

// This will only have effect on Windows with MSVC
#ifdef _MSC_VER
    #define _CRT_SECURE_NO_WARNINGS 1
    #define restrict __restrict
#endif

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdint.h>
#include <errno.h>

int64_t my_getline(char **restrict line, size_t *restrict len, FILE *restrict fp) {
    // Check if either line, len or fp are NULL pointers
    if(line == NULL || len == NULL || fp == NULL) {
        errno = EINVAL;
        return -1;
    }
    // Use a chunk array of 128 bytes as parameter for fgets
    char chunk[128];

    // Allocate a block of memory for *line if it is NULL or smaller than the chunk array
    if(*line == NULL || *len < sizeof(chunk)) {
        *len = sizeof(chunk);
        if((*line = malloc(*len)) == NULL) {
            errno = ENOMEM;
            return -1;
        }
    }

    // "Empty" the string
    (*line)[0] = '\0';

    while(fgets(chunk, sizeof(chunk), fp) != NULL) {
        // Resize the line buffer if necessary
        size_t len_used = strlen(*line);
        size_t chunk_used = strlen(chunk);

        if(*len - len_used < chunk_used) {
            // Check for overflow
            if(*len > SIZE_MAX / 2) {
                errno = EOVERFLOW;
                return -1;
            } else {
                *len *= 2;
            }
            if((*line = realloc(*line, *len)) == NULL) {
                errno = ENOMEM;
                return -1;
            }
        }

        // Copy the chunk to the end of the line buffer
        memcpy(*line + len_used, chunk, chunk_used);
        len_used += chunk_used;
        (*line)[len_used] = '\0';

        // Check if *line contains '\n', if yes, return the *line length
        if((*line)[len_used - 1] == '\n') {
            return len_used;
        }
    }

    return -1;
}

const char* getfield(char* line, int num) {
    const char* tok;
    for (tok = strtok(line, ","); tok && *tok; tok = strtok(NULL, ",\n")) {
      if (!--num)
          return tok;
    }
    return NULL;
}

int main(void) {
    FILE *fp = fopen("ccc.csv", "r");
    if(fp == NULL) {
        perror("Unable to open file!");
        exit(1);
    }

    char *line = NULL;
    size_t len = 0;

    while(my_getline(&line, &len, fp) != -1) {
        char* tmp = strdup(line);
        printf("Field 4 would be %s\n", getfield(tmp, 4));
        free(tmp);
    }

    fclose(fp);
    free(line);
}