How to use fopen in C - c

Question

I have problems using fopen() in c.
When I compile and run this:
const char* mode="r";
FILE* imgstream = fopen(pathinput, mode);
I am getting a Segmentation fault:
main called
argv[1]: /home/student/workspace/Flip/res/test.pbm
open mode: r
./testscript: line 6: 12454 Segmentation fault ./flippr /home/student/workspace/Flip/res/test.pbm /home/student/workspace/Flip/test_out.pbm
It appears to me that it should be working ...
What am I doing wrong?
the whole code of main.c :
#include "flip.h"
#include "img.h"
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
int pbm_image_flip(PbmImage* image){
return 0;
}
int main(int argc, char **argv) {
#ifdef DEBUG
printf("main called\n");
#endif
int* error=RET_PBM_OK;
#ifdef DEBUG
printf("argv[1]: %s\n", argv[1]);
#endif
const char* mode="r";
#ifdef DEBUG
printf("open mode: %s\n", mode);
#endif
FILE* imgstream = fopen(argv[1], mode);
#ifdef DEBUG
printf("imgstream fopen");
#endif
PbmImage* pbmimage=pbm_image_load_from_stream(imgstream, error);
pbm_image_flip(pbmimage);
return 0;
}
The code runs until before I try to fopen the stream.

Answer 1

The error comes from this line:
const char* mode='r';
There is a difference between singe and double quotes in C. Single are for characters, double for string literals (which can be safely assigned to char*)
The solution for you would be
FILE* imgstream = fopen(pathinput,"r");

Answer 2

There is still one problem:
int* error = RET_PBM_OK;
will crash or will lead to a crash later. You are using an uninitialized pointer.
Write this:
int error = RET_PBM_OK ;
...
PbmImage* pbmimage=pbm_image_load_from_stream(imgstream, &error);
But this is bad practice. Normally pbm_image_load_from_stream shoud take care of setting error to RET_PBM_OK if it succeeds. In that case you don't even need to initialize error before calling pbm_image_load_from_stream.