My c method crashes my program

[AussieGuy69]

This function crashes my program with
*** glibc detected *** gnutella: corrupted double-linked list: 0x08835df8 ***
======= Backtrace: =========
/lib/tls/i686/cmov/libc.so.6[0xb7744d81]
/lib/tls/i686/cmov/libc.so.6(__libc_malloc+0x8d)[0xb7745cad]
/usr/lib/libglib-2.0.so.0(g_malloc+0x2d)[0xb79afdcd]


My code is below:
void add_alternate_source(char filename[]) {
int *file_size;
int sha1;
struct stat *file_stat;

//initalise file stats
printf("\nGetting file statistics for %s \n", filename); //works, prints out fine
int result = stat(filename, file_stat);

//get file size
printf("\n Size of file: %u\n", file_stat->st_size); //works, prints file size fine.

//get file sha1


//add X-Alternate-Location

}


int main() {

gchar *filename = "/home/myusername/shared/testfile";
add_alternate_source(filename);

}

any idea what I might be doing wrong?

[WW]

The second argument to the stat() function should be a pointer to an existing block of memory containing a stat structure. You haven't allocated this memory.

[AussieGuy69]

so. allocate the memory with alloc() for the pointer file_stat then free the object after im finished?.

[WW]

Or just declare


struct stat file_stat;

and change the subsequent use of file_stat as appropriate.

[AussieGuy69]

Ive done that, now the program works fine.

coming from a java background I read up on memory allocation, wrote a little test program then allocated the memory properly for the size of the struct stat.

I also freed file_stat afterwards because the function will be called no less than a thousand times.

[dribeas]

I also freed file_stat afterwards because the function will be called no less than a thousand times.

You can use stack allocated memory and get a pointer to your struct as @WW pointed out(which is the common usage):



struct stat file_stat;
int result = stat(filename, &file_stat);


While memory allocation is really fast in Java due to the implementation of moving garbage collectors, in non-managed languages allocation is more expensive as the system must find a suitable piece of memory. This is also not needed, as you can use local variables as above (which Java does not have).

Learning a language is not getting to know the syntax, but also the idioms that the language or experience enforces.