Thread: Need help with program that crashes - probably an allocation problem

Hello everyone , i have tried everything (or so i think) to solve this problem and keep the program logic intact (allocate memory dynamically while everything is unknown [string length and array size alike]).The problem seems to be happening at function GetDirectoryFiles(...) , where i believe i am making some mistake with the allocation of memory , but i just cant find it.The program should take an unknown size string from the user (movies directory / path) , then it should open and read the directory if it exists and then store all the names of the files(filenames) that exist in this directory.

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <dirent.h>


#define INITIAL_STRING_SIZE 64
#define INITIAL_STRING_ARRAY_SIZE 16


char* ReadDirectory();
char** GetDirectoryFiles(char *directory,int *numberoffiles);
void DeleteDirectory(char **dir);
void DeleteFilenames(char ***filenames,int size);
char* ReallocOrFreeString(char *sp,size_t sz);
void ErrorMessage(const char *msg);


int main()
{
    int number,i;
    char *maindir = NULL,**mainfilenames = NULL;


    maindir = ReadDirectory();


    mainfilenames = GetDirectoryFiles(maindir,&number);


    for(i=0;i<number;i++)
    {
        printf("%s\n",mainfilenames[i]);
    }


    DeleteDirectory(&maindir);
    DeleteFilenames(&mainfilenames,number);


    system("PAUSE");
    return 0;
}


char* ReadDirectory()
{
    int c,size = 0,allocated = INITIAL_STRING_SIZE;
    char *maindir = NULL;


    maindir = malloc(allocated * sizeof(char));


    if(maindir == NULL)
    {
        ErrorMessage("ReadDirectory 1");
    }


    printf("Give the directory where the movies are: ");


    while((c = getchar()) != EOF && c != '\n')
    {
        if(size == allocated - 1)
        {
            maindir = ReallocOrFreeString(maindir,(allocated *= 2) * sizeof(char));


            if(maindir == NULL)
            {
                ErrorMessage("ReadDirectory 2");
            }
        }


        maindir[size] = c;


        size++;
    }


    maindir[size] = '\0';


    return ReallocOrFreeString(maindir,size+1);
}


char** GetDirectoryFiles(char *directory,int *numberoffiles)
{
    char **filenames = NULL;
    struct dirent *dent;
    DIR *dir;
    int i;


    if((dir = opendir(directory)) == NULL)
    {
        ErrorMessage("GetDirectoryFiles 1");
    }


    *numberoffiles = 0;


    while((dent = readdir(dir)) != NULL)
    {
        if(!strcmp(dent->d_name,".") || !strcmp(dent->d_name,".."))
        {
            continue;
        }


        (*numberoffiles)++;
    }


    filenames = malloc(*numberoffiles * sizeof(char*));


    if(filenames == NULL)
    {
        ErrorMessage("GetDirectoryFiles 2");
    }


    closedir(dir);


    if((dir = opendir(directory)) == NULL)
    {
        ErrorMessage("GetDirectoryFiles 1");
    }


    while((dent = readdir(dir)) != NULL)
    {
        if(!strcmp(dent->d_name,".") || !strcmp(dent->d_name,".."))
        {
            continue;
        }


        filenames[*numberoffiles] = malloc((strlen(dent->d_name) + 1) * sizeof(char));


        if(filenames[*numberoffiles] == NULL)
        {
            ErrorMessage("GetDirectoryFiles 3");
        }


        strcpy(filenames[*numberoffiles],dent->d_name);
    }


    closedir(dir);


    for(i=0;i<*numberoffiles;i++)
    {
        printf("%s\n",filenames[i]);
    }


    return filenames;
}


void DeleteDirectory(char **dir)
{
    free(*dir);
    *dir = NULL;
}


void DeleteFilenames(char ***filenames,int size)
{
    int i;


    for(i=0;i<size;i++)
    {
        free((*filenames)[i]);
    }


    free(*filenames);
    *filenames = NULL;
}


char* ReallocOrFreeString(char *sp,size_t sz)
{
    char *p;


    p = realloc(sp,sz);


    if(p == NULL)
    {
        free(sp);
    }


    return p;
}


void ErrorMessage(const char *msg) {
    fprintf(stderr, "Error: %s\n", msg);
    exit(EXIT_FAILURE);
}

Originally Posted by Salem

Well let me leave this gdb run for you to ponder over.

Code:

$ gdb -q ./a.out
Reading symbols from ./a.out...done.
(gdb) run
Starting program: /home/sc/Documents/a.out 
Give the directory where the movies are: .

Program received signal SIGSEGV, Segmentation fault.
strlen () at ../sysdeps/x86_64/strlen.S:106
106    ../sysdeps/x86_64/strlen.S: No such file or directory.
(gdb) bt
#0  strlen () at ../sysdeps/x86_64/strlen.S:106
#1  0x00007ffff7a7d69c in _IO_puts (str=0x0) at ioputs.c:35
#2  0x0000000000400d78 in GetDirectoryFiles (directory=0x603010 ".", numberoffiles=0x7fffffffddf0)
    at foo.c:165
#3  0x0000000000400a0e in main () at foo.c:28
(gdb) up
#1  0x00007ffff7a7d69c in _IO_puts (str=0x0) at ioputs.c:35
35    ioputs.c: No such file or directory.
(gdb) up
#2  0x0000000000400d78 in GetDirectoryFiles (directory=0x603010 ".", numberoffiles=0x7fffffffddf0)
    at foo.c:165
165            printf("%s\n",filenames[i]);
(gdb) print i
$1 = 0
(gdb) print filenames[i]
$2 = 0x0
(gdb) print *numberoffiles
$3 = 1354

Thank you for your help (btw i like your reply , because it should make me find my fault on my own) , howewer i dont know how to read that , nor do i know were to learn to read it.

Salem was using a program called gdb to track down the source of your crash. The output he has posted is called a backtrace, which is basically a listing of all the function calls made up to the point of the crash.

With a little bit of googling there are explanations of gdb out there.
RMS's gdb Tutorial: How do I use the call stack?

The output Salem gave you should help you with the problem... you'll have to fix the filenames array to get anywhere close to a fix.