pointer to char changes after opendir() system call

Question

i am currently trying to delete directories from system call using c and i am facing a weird problem. In my deleteFunction() after using the char * path to open the directory. the value of path changes

here is part of the code:

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

void deleteDir(char *path){
    //opening the directory
    printf("BEFORE %s\n",path );
    DIR *p = opendir(path);
    if (p == NULL){
        printf("Directory not Opened!\n");
        exit(2);
    }
    printf("AFTER %s\n",path );
}

void main(int argc,char *argv[]){

    if (argc != 2){
        printf("Not enough Arguments!\n");
        exit(1);
    }

    //creating the path 
    char * currentDir = getcwd(NULL,0);
    strcat(currentDir,"/");
    strcat(currentDir,argv[1]);
    //deleting the directory
    deleteDir(currentDir);
    exit(0);
}

the output produced is:

BEFORE /home/tarounen/test/newfolder
AFTER /home/tarounen/test/!�

note: i am only taking the directory name as parameter

`main` returns `int`, not `void`. (That's not the cause of your problem.) — Keith Thompson, Feb 24 '15 at 20:39

score 3 · Accepted Answer · answered Feb 24 '15 at 20:45

The getcwd function is probably allocating just enough space to hold the current path, so adding more characters with strcat overflows the buffer, and results in undefined behavior. Try this

char path[MAXPATHLEN];
getcwd( path, MAXPATHLEN );
strcat( path, "/" );
strcat( path, argv[1] );

score 3 · Answer 2 · answered Feb 24 '15 at 20:45

getcwd only allocates enough memory to hold the directory when you pass NULL.
Concatenating to its result has undefined behaviour.

If you want to use strcat, you need to provide your own buffer with enough space:

char buffer[MAXPATHLEN] = {0};
if (getcwd(buffer, sizeof(buffer)))
{
    strcat(buffer, "/");
    strcat(buffer, argv[1]);
    deleteDir(buffer);
}

pointer to char changes after opendir() system call

2 Answers2