How to do proper error handling with the fopen function - c

Question

I wrote a program that asks the user to enter the full pathname of a file. It will then attempt to open that file from the pathname string provided. I used the standard error checking that most books have recommended, which is to close the program if fopen() returns NULL (which it will do in the case that the file does not exist). When I run the program and enter some random characters when prompted (obviously not a valid filename) my program hangs with a runtime error because it's trying to open that file that doesn't exist.
What is the point of the standard error check (pfile == NULL) if your program has already crashed when it calls fopen()? See below code.
I'm using LabWindows CVI 2017 as my enfironment which uses the clang compiler. See image of run time error.
#include <stdio.h>
#include <string.h>
#define MAX 200
int main (void){
char buffer[MAX];
int len = 0;
FILE *pfile = NULL;
printf("please enter the full pathname of the file you wish to process.\n");
fgets(buffer, MAX, stdin);
len = strlen(buffer);
buffer[len - 1] = '\0';
pfile = fopen(buffer, "r");
if(pfile == NULL){
printf("not a valid filename, press any key to exit.");
getchar();
return -1;
}
int sum = 0;
int c = 0;
while((c = fgetc(pfile)) != EOF){
sum += sizeof(c);
}
printf("the size of your file is %d\n", sum);
getchar();
return 0;
}

Answer 1

You are doing the proper error handling. Your program is valid in that respect. However, your IDE does some extra error checking, which is the cause of the behavior you're seeing.

Answer 2

The usual rules for error checking in these sorts of situations are:
Do check for error returns. (You're doing that.)
Do print a useful error message. (You're doing that.)
Print error messages to stderr.
If the error involves a file, do include the filename in the error message.
If the error involves a function that sets errno, do print the "perror" text" ("No such file or directory", etc.).
If you're writing a tool that will be combined into larger scripts, do include the program's name in the error message.
If the error occurs due to an input file you're reading, do print the name of that file and the line number.
Adopting rules 1 through 6, an improved version of your error check would be
if(pfile == NULL) {
fprintf(stderr, "%s: can't open %s: %s\n", progname, buffer, strerror(errno));
return EXIT_FAILURE;
}
For this to work you'll need both of:
#include <string.h>
#include <errno.h>
If that's too much work, a simpler way is just to call
perror(buffer);
although this falls down somewhat on rules 2, 6, and 7.