Why does setting a breakpoint make my code work?

Question

I am very new to C , so I'm sure I'm doing inconvenience, but it puzzles me.

My code should get a header from the user and create a folder in the route directory with that name. It only works if I set a breakpoint in the implementation of makeFolder() . For some reason, taking a little rest before I click continue makes it work (I use Xcode).

It does not work, I mean that it correctly returns 0, but the folder is not created.

This is one of my first attempts to do anything with C , and I just messed around with it, trying to learn it.

Edit Thank you very much for your answers and comments. Now it works as expected, and I learned a bit of it. You are all scientists and gentlemen.

 #include <stdio.h> #include <stdlib.h> #include <sys/stat.h> #include <sys/types.h> #include <string.h> #define MAX_TITLE_SIZE 256 void setTitle(char* title) { char *name = malloc (MAX_TITLE_SIZE); printf("What is the title? "); fgets(name, MAX_TITLE_SIZE, stdin); // Remove trailing newline, if there if(name[strlen(name) - 1] == '\n') name[strlen(name) - 1] = '\0'; strcpy(title, name); free(name); } // If I set a breakpoint here it works void makeFolder(char * parent, char * name) { char *path = malloc (MAX_TITLE_SIZE); if(parent[0] != '/') strcat(path, "/"); strcat(path, parent); strcat(path, "/"); //strcat(path, name); //strcat(path, "/"); printf("The path is %s\n", path); mkdir(path, 0777); free(path); } int main (int argc, const char * argv[]) { char title[MAX_TITLE_SIZE]; setTitle(title); printf("The title is \'%s\'", title); makeFolder(title, "Drafts"); return 0; } 

Answer 1

The malloc'd variable path contains garbage because you never fill it. Running this code in the debugger may cause it to accidentally see zeroed memory, which then will accidentally give the expected results.

You should at least set the first path character to a leading zero as follows:

 path[0] = '\0'; 

Otherwise, concat() may not work as concat() .