Question

It’s been a very long time since I coded in C, and I’ve spent about two hours googling how to properly use fscanf. As far as I can tell, this code is correct, but I’m getting EXC_BAD_ACCESS every time I run it:

int rasterWidth;
int rasterHeight;
FILE* f = fopen("scene.u2d","r");

if (f == NULL)
{
    perror("Can't open file!");
}

char m [2];
fscanf(f, "%s", m);
fscanf(f, "%d %d",&rasterWidth,&rasterHeight); // Getting EXC_BAD_ACCESS here

printf("%s %d %d",m,rasterWidth,rasterHeight);

I’ve verified that XCode is opening the proper file (it loads the first two chars correctly). scene.u2d looks like this:

U2
500 500
-1.0 -1.0 1.0 1.0
g triangle.raw
c 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1
s 0.5 1.0
t 0.3 -0.2

Is there something obvious that I’m doing wrong? Thanks!

Answer 1

First, the man page for scanf says:

s Matches a sequence of non-white-space characters; the next pointer must be a pointer to character array that is long enough
to hold the input sequence and the terminating null character ('\0'), which is added automatically. The input string stops
at white space or at the maximum field width, whichever occurs first.

This means you need at least char m[3] for that input file because of the null terminator.

I would also recommend using %2s as your format specifier so you don’t overflow the buffer.

---

If that’s not the problem, have you tried running only the code snippet you posted? It works for me – I suspect there’s some memory mismanagement before the posted code. Or, is your code actually something like:

int *rasterWidth, *rasterHeight;

fscanf(f, "%d %d",rasterWidth,rasterHeight); // this is definitely a bad access 

Bad accesses are on scanf calls are often caused by passing uninitialised pointers in.