Question

This is my code. I need create 10 files with this format:

0.txt
1.txt
…

But I can’t do it, the result is different. Can anyone help?

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


char* direccion(char *dirD,int number){
    char buffer[100];
    char *n;
    char *q;
    char* formato=".txt";

    sprintf(buffer, "%i", number);
    n= strcat(dirD,buffer);
    q= strcat(n,formato);

    return q;

}
int main(){
    int u;
    int number= 0;
    int t= 0;
    char* q = "e:/c9/";
    for(t=0; t< 10 ; t++){

        char* dir = direccion(q,number);

            if(fopen(dir,"w")){
                fopen(dir,"w");
                u=1;
            }
            else{
                u=0;
                printf("Error\n");
            }
        number++;

    }
    return 0;
}

Thanks !

Answer 1

Problem No 1. is:

char *q = "e:/c9/";
for(t = 0; t < 10; t++)
{
    char *dir = direccion(q, number);
}

The variable q is a string literal. However, in the function direccion(), you pass it as the first argument to strcat(), which tries to modify it — BOOM, a segfault. Solution:

char buf[1000];
strcpy(buf, "e:/c9/");
char *dir = direccion(buf, number);

Problem #2 is as @Charlie Martin pointed out is that you return a statically automatically allocated local string, which is invalid after the direccion() function returns. Maybe

return strdup(buffer);

in this case; don’t forget to free it after use.

Edit: seems you don’t even ask about this. You can create a file using the open() system call (function):

#include <fcntl.h>
#include <stdio.h>

int fd = open("file.txt", O_RDWR | O_CREAT, 0644);
close(fd);

Of course substitute the actual file mode you want for 0644 (but don’t make the file executable unless it contains a program to be executed).

Edit 2: I didn’t even catch this one… So, in the for loop, you want to reset the base filename over and over:

for (yadda yadda)
{
    strcpy(buf, "e:/c9/");
    char *dir = direccion(buf, i);
}

etc.