Why am I getting memory leaks even though I freed my allocations with free in C

Question

I have found similar questions to mine here is StackOverFlow but I couldn't find a solution to my exact case.

I am trying to take user input as commands to execute them using getline function in C, so I allocated memory for a buffer to hold the input char *buffer, and I allocated an array of pointers to be passed to execve to execute the command char **p_buffer with p_buffer[0] = buffer, and then I call fork : so I can call execve in the child process only, at the bottom of my code a called free two time : one for buffer and one for p_buffer

but when I use valgrind to check for memory leaks I get:

==102098== HEAP SUMMARY:
==102098==     in use at exit: 100 bytes in 1 blocks
==102098==   total heap usage: 5 allocs, 4 frees, 5,356 bytes allocated
==102098==
==102098== 100 bytes in 1 blocks are definitely lost in loss record 1 of 1
==102098==    at 0x483B7F3: malloc (in /usr/lib/x86_64-linux- 
gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
==102098==    by 0x1092F0: create_buffers (functions.c:15)
==102098==    by 0x109431: main (shell.c:23)
==102098==
==102098== LEAK SUMMARY:
==102098==    definitely lost: 100 bytes in 1 blocks
==102098==    indirectly lost: 0 bytes in 0 blocks
==102098==      possibly lost: 0 bytes in 0 blocks
==102098==    still reachable: 0 bytes in 0 blocks
==102098==         suppressed: 0 bytes in 0 blocks
==102098==
==102098== For lists of detected and suppressed errors, rerun with: -s
==102098== ERROR SUMMARY: 1 errors from 1 contexts (suppressed: 0 from 0)

this is My code:

 25         while (mode)
 26         {
 27                 mode = isatty(STDIN_FILENO);
 28                 if (mode)
 29                         write(STDOUT_FILENO, "#cisfun$ ", 9);
 30                 if (getline(&buffer, &i, stdin) == -1)
 31                         perror("Failed to read from stdin"), exit(2);
 32                 for (j = 0; buffer[j] != '\n'; j++){}; /* these two lines are just to remove the */
 33                 buffer[j] = '\0', p_buffer[0] = buffer; /* newline char at the end of buffer */
 34                 my_pid = fork();
 35                 if (!my_pid)
 36                 {
 37                         if (execve(p_buffer[0], p_buffer, env) == -1)
 38                                 perror(av[0]);
 39                 }
 40                 else
 41                         wait(NULL);
 42         }
 43         free(p_buffer);
 44         free(buffer);

It would help to see the allocations as well. Line 23, in particular. — Scott Hunter, Aug 26 '22 at 14:59
The problem is that Valgrind doesn't share your sense of confidence. — Paul Floyd, Aug 26 '22 at 15:03
More seriously, think about what fork does exactly and the flow of the child process. — Paul Floyd, Aug 26 '22 at 15:10
@PaulFloyd fork seems irrelevant, since it immediately execs, so it discards its copy of the heap. — Barmar, Aug 26 '22 at 15:19
Hmm yes https://stackoverflow.com/questions/5429141/what-happens-to-malloced-memory-after-exec-changes-the-program-image so it's just the parent leaking — Paul Floyd, Aug 26 '22 at 15:24
Needs a [mcve]. How are `buffer`, `p_buffer` and `i` declared and initialized? — Shawn, Aug 26 '22 at 22:23
(also, `getline()` returns the number of chars read; that tells you where the newline (if any) is; no need to loop through the string looking for one) — Shawn, Aug 26 '22 at 22:25

Why am I getting memory leaks even though I freed my allocations with free in C

0 Answers0