Question

I have created a function that creates a dynamic string array with dynamic string length and then I return it to my main function. Everything works fine inside my function but when I try to print the array in main I get a segmentation fault after the 4th string – first two string don’t print out correct either. This part of the program is supposed to find out all entries in a directory and its sub-directories and store them in main memory.

Here’s the result:

Path[0]=A/New Folder. - i=0
Path[1]=A/atext - i=1
Path[2]=A/a - i=2
Path[3]=A/alink - i=3
Path[4]=A/afolder - i=4
Path[5]=A/afolder/set008.pdf - i=0
Path[6]=A/afolder/anotherfolder - i=1
Path[7]=A/afolder/anotherfolder/folderOfAnotherFolder - i=0
Path[8]=A/afolder/anotherfolder/folderOfAnotherFolder/mytext - i=0
Path[9]=A/afolder/anotherfolder/mytext - i=1
Path[10]=A/afolder/set001.pdf - i=2
Entries in directory: A
��
��
A/a
A/alink
Segmentation fault

And here’s the code:
function:

char ** getDirContents(char *dirName,char **paths ) 
{   
    DIR * tmpDir;
    struct dirent * entry;
    //char  tmpName[512];
    char * tmpName=NULL;
    struct stat node;
    int size=0;
    int i=0;
    //paths=NULL;

    if((tmpDir=opendir(dirName))==NULL){
        perror("getDirContents opendir"); 
        return NULL;
    }
    i=0;
    while ((entry=readdir(tmpDir))!=NULL) 
    {
        //if (entry->d_ino==0) continue;
        if(strcmp(entry->d_name, ".") == 0 || strcmp(entry->d_name, "..") == 0)//Ignore root & parent directories
            continue;but I

        tmpName =(char *)malloc(strlen(dirName)+strlen(entry->d_name)+2);
        strcpy(tmpName,dirName);
        strcat(tmpName,"/");
        strcat(tmpName,entry->d_name);
        //printf("\ntmpName[%d]:%s",count,tmpName);

        paths=(char**)realloc(paths,sizeof(char*)*(count+1));
        paths[count]=NULL;
        //paths[count]=(char*)realloc(paths[count],strlen(tmpName)+1);
        paths[count]=(char*)malloc(strlen(tmpName)+1);

        //memcpy(paths[count],tmpName,strlen(tmpName)+1);
        strcpy(paths[count],tmpName);
        printf("\nPath[%d]=%s - i=%d",count,paths[count],i);

        count++;

        if(lstat(tmpName,&node)<0)    
            { 
                printf("\ntmpName:%s",tmpName);
                perror("getDirContents Stat");
                exit(0);
            }
        if (S_ISDIR(node.st_mode))
            {
                getDirContents(tmpName,paths);//Subfolder
            }

        //printf("\n%s,iters:%d",tmpName,i);
        free(tmpName);
        tmpName=NULL;
        i++;
    }
close(tmpDir);
return(paths);
}

main:

char **A=NULL;
count=0;
A=getDirContents(dir1,NULL);
Aentries=count;
count=0;
//B=getDirContents(dir2,NULL);
printf("\nEntries in directory: %s",dir1);
for(i=0;i<Aentries;i++)
{
     printf("\n%s",A[i]);
}

count is a global variable

I just can’t figure out what is wrong I think I use the return command properly. I also tried the same code with paths as a global variable and it worked fine (main printed out the correct results).
I have a feeling it has something to do with the recursive call of my function

Answer 1

Your code has an Undefined Behavior.

You call the function as:

A=getDirContents(dir1,NULL);

and the function is defined as:

char ** getDirContents(char *dirName,char **paths ) 

Further you call realloc on paths.

paths=(char**)realloc(paths,sizeof(char*)*(count+1));

This causes Undefined Behavior.

The standard mandates that the pointer being passed to realloc should exactly match the pointer which was allocated dynamic memory using a memory management function. Memory management functions specified by the standard are:
aligned_alloc, calloc, malloc, and realloc.

The pointer(paths) you are passing to realloc() was not returned by any of these and hence the Undefined Behavior.