How to open file in C program? - c

Question

The code here is a code from a website. Since I was facing an issue with my origin code, I ended up trying this implementation from a website. But turns out I have the same issue with this program too
#include <stdio.h>
#include <stdlib.h>
int main()
{
int num;
FILE *fptr;
if ((fptr = fopen("D:\\TestFile\\test.txt","r")) == NULL){
printf("Error! opening file\n");
perror(fptr);
// Program exits if the file pointer returns NULL.
exit(1);
}
fscanf(fptr,"%d", &num);
printf("Value of n=%d\n", num);
printf("%s\n", fptr);
fclose(fptr);
return 0;
}
I am stuck with the if condition i.e., whatever I do I am not able to read the file except the root directory. Even though I specify the path, it still looks for the file under root directory.
I am not sure why it's not working, provided the same code works fine in Linux

Answer 1

I see 2 mistakes, the one related to perror mentioned in the comments, and the last printf. Now if the program is still not working, it could be interesting to check the error or to get the program output.
#include <stdio.h>
#include <stdlib.h>
int main()
{
int num;
FILE *fptr;
if ((fptr = fopen("D:\\TestFile\\test.txt","r")) == NULL){
// printf("Error! opening file\n");
// perror(fptr); // MISTAKE-1: perror parameter is a string
perror("Error! opening file");
// Program exits if the file pointer returns NULL.
exit(1);
}
fscanf(fptr,"%d", &num);
printf("Value of n=%d\n", num);
//printf("%s\n", fptr); // MISTAKE-2: fptr is not a string
fclose(fptr);
return 0;
}

Answer 2

the posted code does not cleanly compile!
Here is the results of compiling with many of the warnings enabled:
gcc -ggdb3 -Wall -Wextra -Wconversion -pedantic -std=gnu11 -c "untitled1.c" -o "untitled1.o"
untitled1.c: In function ‘main’:
untitled1.c:11:16: warning: passing argument 1 of ‘perror’ from incompatible pointer type [-Wincompatible-pointer-types]
11 | perror(fptr);
| ^~~~
| |
| FILE * {aka struct _IO_FILE *}
In file included from untitled1.c:1:
/usr/include/stdio.h:775:33: note: expected ‘const char *’ but argument is of type ‘FILE *’ {aka ‘struct _IO_FILE *’}
775 | extern void perror (const char *__s);
| ~~~~~~~~~~~~^~~
untitled1.c:19:13: warning: format ‘%s’ expects argument of type ‘char *’, but argument 2 has type ‘FILE *’ {aka ‘struct _IO_FILE *’} [-Wformat=]
19 | printf("%s\n", fptr);
| ~^ ~~~~
| | |
| | FILE * {aka struct _IO_FILE *}
| char *
Compilation finished successfully.
Note; the statement: Compilation finished successfully. just means the compiler applied some work around to each of the problems. It does NOT mean the correct code was produced.