Command line output reader

cl_reader.c

#define _POSIX_C_SOURCE 2 // to allow popen and pclose.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

struct cl_reading {
    char **output;
    int malloc_error;
    int n_lines;
    int pclose_error;
    int popen_error;
    int realloc_error;
};

void free_cl_reading(struct cl_reading *reading)
{
    for (int i = 0; i < reading->n_lines; i++)
        free(reading->output[i]);
    free(reading->output);
    free(reading);
}

struct cl_reading *read_cl_output(char *cmd, unsigned int max_lines, unsigned int max_line_len)
{
    struct cl_reading *reading = malloc(sizeof(*reading));
    FILE *fp;
    char buf[max_line_len];
    unsigned int n_lines = 0;
    int pclose_status;

    reading->output = malloc(sizeof(*reading->output));
    fp = popen(cmd, "r");
    if (fp == NULL) {
        reading->popen_error = 1;
        return reading;
    }
    while (fgets(buf, max_line_len + 1, fp) && n_lines < max_lines) {
        if (*buf == '\n') {
            // for when max_line_len < line to be printed.
            continue;
        }
        reading->output[n_lines] = malloc(sizeof(buf));
        if (reading->output[n_lines] == NULL) {
            reading->malloc_error = 1;
            return reading;
        }
        // trims out the new line character
        buf[strcspn(buf, "\n")] = 0;
        strcpy(reading->output[n_lines++], buf);
        reading->output = realloc(reading->output, (n_lines + 1) * sizeof(*reading->output));
        if (reading->output == NULL) {
            reading->realloc_error = 1;
            return reading;
        }
    }
    pclose_status = pclose(fp);
    if (pclose_status == -1) {
        reading->pclose_error = 1;
        return reading;
    }
    reading->n_lines = n_lines;
    return reading;
}