[SOLVED] getline() output null when passed a pointer from outer function in c

Issue

I'm trying to read line from a file, when i use getline directly in the batch_mode function it works fine but when i refactor the code in a separate function it gives me a error.

int main(int argc, char *argv[]) {
  if (argc > 2)
    return EXIT_FAILURE;

  batch_mode(argv[1]);

  return EXIT_SUCCESS;
}

batch_mode function

void batch_mode(char *path) {
  char *line = NULL;
  ssize_t error = 0;
  char *cmd = NULL;
  FILE *file = fopen(path, "r");

  if (file == NULL) {
    printf("Coudn't read file\n");
    return;
  }

  while (error != -1) {
    read_line(line, file, cmd);
    error = -1;

    int thread = fork();

    if (thread == 0) {
      char *myargs[] = {NULL};

      execv(cmd, myargs);
    } else {
      thread = wait(NULL);
    }
  }

  if (file != NULL)
    fclose(file);
  free(line);
}

lines are read correctly in this function when printf but output null in the batch_mode function

ssize_t read_line(char *line, FILE *file, char *cmd) {
  size_t len = 0;
  ssize_t read = 0;

  read = getline(&line, &len, file);

  printf("%s\n", line);
  if (read == -1) {
    printf("Coudn't read line\n");
    return -1;
  }

  char *copy = line;
  cmd = strsep(&copy, " ");
  printf("%s\n", cmd);

  return 0;
}

and when trying this code it outputs that it can't read the file because it's executing more than once

void batch_mode(char *path) {
  char *line = NULL;
  ssize_t error = 0;
  char *cmd = NULL;
  FILE *file = fopen(path, "r");

  if (file == NULL) {
    printf("Coudn't read file\n");
    return;
  }

  while ((error = read_line(line, file, cmd)) != -1) {

    int thread = fork();

    if (thread == 0) {
      char *myargs[] = {NULL};

      execv(cmd, myargs);
    } else {
      thread = wait(NULL);
    }
  }

  if (file != NULL)
    fclose(file);
  free(line);
}

Solution

Code has at least these problems:

Never frees memory

read = getline(&line, &len, file); allocates memory to line. Code never frees it.

The calling code's free(line); is not the updated line of read_line().

Updating only local copy

cmd = strsep(&copy, " "); does not update the calling code's cmd.

Calling code is doing execv(NULL, myargs);

---

Instead, pass the address of the pointer. Perhaps

ssize_t read_line(char **line, FILE *file, char **cmd) {

Answered By - chux - Reinstate Monica

Answer Checked By - Dawn Plyler (WPSolving Volunteer)