Why do I get a still reachable block after mallocing a char*? - c

Question

I have the following code:
#include <stdio.h>
#include <ctype.h>
#include <string.h>
#include <stdlib.h>
#include <sys/stat.h>
void print_usage()
{
printf("%s\n", "usage");
}
int file_exist (char *filename)
{
struct stat buffer;
return (stat (filename, &buffer) == 0);
}
int parse_parameters(int argc, char *argv[], char** in)
{
unsigned int i1 = 1; // 0 is the filename
for (; i1 < argc; ++i1)
{
if( 0 == strcmp("-h", argv[i1]) )
{
print_usage();
return 0;
}
else if( 0 == strcmp("-i", argv[i1]) )
{
*in = malloc( sizeof(char) * strlen(argv[++i1]) + 1 );
strcpy(*in, argv[i1]);
continue;
}
else
{
print_usage();
return 1;
}
}
return 0;
}
int main(int argc, char *argv[])
{
if( argc != 3 )
{
print_usage();
return 0;
}
char* in = NULL;
int parse = parse_parameters(argc, argv, &in);
if ( 0 != parse )
return parse;
printf("in: %s\n", in);
FILE* finput = NULL ;
if (file_exist(in))
finput = fopen(in, "r");
if (finput == NULL) {
perror("fopen");
exit(1);
}
free(in);
fclose(finput);
return 0;
}
After running it with valgrind with following parameters:
./main -i input
I get the following:
==30977== Memcheck, a memory error detector
==30977== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al.
==30977== Using Valgrind-3.10.0.SVN and LibVEX; rerun with -h for copyright info
==30977== Command: ./main -i input
==30977==
in: input
fopen: No such file or directory
==30977==
==30977== HEAP SUMMARY:
==30977== in use at exit: 6 bytes in 1 blocks
==30977== total heap usage: 2 allocs, 1 frees, 574 bytes allocated
==30977==
==30977== 6 bytes in 1 blocks are still reachable in loss record 1 of 1
==30977== at 0x4C2AB80: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==30977== by 0x400946: parse_parameters (main.c:31)
==30977== by 0x4009E7: main (main.c:54)
==30977==
==30977== LEAK SUMMARY:
==30977== definitely lost: 0 bytes in 0 blocks
==30977== indirectly lost: 0 bytes in 0 blocks
==30977== possibly lost: 0 bytes in 0 blocks
==30977== still reachable: 6 bytes in 1 blocks
==30977== suppressed: 0 bytes in 0 blocks
==30977==
==30977== For counts of detected and suppressed errors, rerun with: -v
==30977== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)
Why is that ? If I try to pass in as char* then it won't get changed after the parse_parameters function.

Answer 1

Your program is exiting as a result of the exit (1) call, which occurs before you free (in). As a result you are seeing the valgrind message.