Question

Heres my code:

void *PrintLine(void *line)
{
    printf("Line: #%s\n", (char *)line);
    pthread_exit(NULL);
}

int main (int argc, char *argv[])
{
    char line[80];
    while(fgets(line,sizeof(line),fp))
    {
        pthread_create(&threads[rt], NULL, PrintLine, (void*)line);
    }
    fclose(fp);
}

Please dont tell me that running a thread only to print a file line doesn’t make sense, I removed a lot of code so its easier to read and understand my problem.

As you would guess this code doesn’t work, what should I do to be able to print/use “line” inside the thread?

Answer 1

You’re passing a pointer to line to the newly created thread, when your thread gets around to use line , perhapse fgets have written something else to it. Or perhaps it’s in the middle of writing something when your thread accesses it.

You can pass a copy of the line you’ve read, remember to free() it when you’re done with it inside you thread.

char *copy_of_line = strdup(line);
if(copy_of_line)
  pthread_create(&threads[rt], NULL, PrintLine, copy_of_line);