Thread: [C help] Function for Dynamic Memory Allocation, realloc() gives segmentation fault

I wrote some code in order to get a file name from the user at the terminal. I tried using realloc but there is an error in memory management that I do not understand. I am not sure if I am incorrectly terminating the string, or if there is another error that I cannot see with my limited C experience. Could anyone instruct me on what errors I have made?

Code:

#include

Code:

<stdio.h>
#include <stdlib.h>
#define CHUNK 4

char *file_name;

char *get_file_name(void) {

     char *line = NULL;
     char *tmp = NULL;
     int char_input = 0;
     size_t size = 0, index = 0;
     size = CHUNK;

     printf("Please enter the file name: \n");

     while(char_input != '\n' && char_input != EOF) {

     char_input = getc(stdin);

          if(size <= index) {
               size += CHUNK;
               tmp = realloc(line, size);
               if (!tmp) {
               free(line);
               line = NULL;
               break;
               }
          line = tmp;
          }

          line[index] = char_input;
          index++;

     }

     line[index] = '\0';

     return line;

     }

int main(void) {

    file_name = get_file_name();

    printf("%s", file_name);


    return 0;
}

Originally Posted by bigearsbilly

It's amazing how few people keep up with new C standards.
getline automatically allocates.

A quick search does not bring up getline in C11, not even in an annex as an optional feature, perhaps borrowing from POSIX getline as it looks like from your example. Could you quote exactly where C11 specifies getline? As it stands, my guess is that you are one of those people who do not keep up with the new C standard, but rather confused POSIX with standard C.

Originally Posted by laserlight

A quick search does not bring up getline in C11, not even in an annex as an optional feature, perhaps borrowing from POSIX getline as it looks like from your example. Could you quote exactly where C11 specifies getline? As it stands, my guess is that you are one of those people who do not keep up with the new C standard, but rather confused POSIX with standard C.

Amazingly enough there is a standard getline, after a fashion. It's included in the TR 24731-2 extension which you activate by defining __STDC_WANT_LIB_EXT2__.

Originally Posted by Prelude

Amazingly enough there is a standard getline, after a fashion. It's included in the TR 24731-2 extension which you activate by defining __STDC_WANT_LIB_EXT2__.

Indeed "after a fashion" since such a technical report specifies a library extension rather than a new part of the C standard library, though I suppose they might get included at some point (as we've certainly seen in C++).

Yes. In conclusion, we shouldn't be suggesting getline without the appropriate caveats (e.g., POSIX standard, or other extension to the standard library) because it is not part of standard C, contrary to your claim.