CODEWITHSUNDEEP
c++visual-c++
Iya
Iya

Reputation: 1

Why I am getting this error "access violation writing location"?

I am trying to write a c++ program to read some data from a file. My code is:

void read_file(const char *foldername) {
    FILE *fp;
    char c;
    const char *filename;
    filename=strcat((char *)foldername, "L1_matrix");
    fp=fopen(filename, "w+");
    if(fp)
        while (fgets((char *)c,512,fp))
            printf("%s", c);
}

int main() {
    read_file("A:\\Project\\Root\\event_1\\");
    getchar();
}

I want to read several files like L2_matrix etc.

But in this I am getting several error like:

  1. Access violation location error(I found this error I get in filename)

  2. The variable 'c' is being used without being initialized.

If anybody can help it will be a great help.

Upvotes: 0

Views: 321

Answers (1)

Deduplicator
Deduplicator

Reputation: 45684

strcat((char *)foldername, "L1_matrix");

strcat takes an in-out parameter pointing to a buffer containing a 0-terminated string, and big enough to store the result, and a pointer to a string.

You give it foldername and assure it that it actually points to a modifiable buffer by casting.
Don't lie!

Similarly for your second error, but the cast is more egregiously wrong:

fgets((char *)c,512,fp)

This reads the uninitialized variable c, thus your "without initialization"-warning, which is UB.
Next, you forcibly convert it to a char*, but never fear: On modern desktops, writing or reading through an integer in the char-range converted to a pointer will segfault.

Upvotes: 1

Related Questions