how to read cmdline file in c code example

Example 1: read files in c

#include<stdio.h>
int main(){
	FILE *in=fopen("name_of_file.txt","r");
	char c;
	while((c=fgetc(in))!=EOF)
		putchar(c);
	fclose(in);
	return 0;
}

Example 2: c read file from command line

You can use as your main function:
int main(int argc, char **argv) 

So, if you entered to run your program:
C:\myprogram myfile.txt

argc will be 2
argv[0] will be myprogram
argv[1] will be myfile.txt

To read the file:
FILE *f = fopen(argv[1], "r");