Problem reading/writting binary files.

Hello,
I've a small program with 4 functions.
The first one reads data from a file and returns it as a string(text_from_file)

Code:

int read_file (char* file_to_open, char* text_from_file){
        FILE *fp;
	char tmp_str[MAX_STR];
if((fp = fopen(file_to_open, "r"))==NULL) {
    	printf("Cannot open file.\n");
    	exit(1);
  	} 
	while (!feof(fp)){		
		fgets(tmp_str,MEGABYTE,fp);
		strcat(text_from_file,tmp_str);	
		}
	fclose(fp);
}

Then that string slightly modified and written into a file. When the which I open is a text file, it works well but if I'm opening binary files it doesn't read the whole file, it only reads and returns a smaller string.
What I'm doing wrong? any help would be appreciated

If it's a binary file, use fread, and don't try to treat the data like a string, because it's not in that case.

also - do not use feof to control loop - read FAQ