.txt file extension in terminal - c

Question

How come when I type in "(filename).txt" as part of one of the argument in terminal my code doesn't run and gives me a segmentation fault (core dumped)? but if I type "(filename)" instead then the code runs perfectly?
#include <stdio.h>
#include <stdlib.h>
int main (int argc, char **argv){
FILE *inFile = fopen(argv[1], "r");
FILE *outFile = fopen(argv[2], "w+");
char ch = fgetc(inFile);
while(ch != EOF){
fputc(ch, outFile);
ch = fgetc(inFile);
}
}
I skipped error checking writing this small sample code of what I mean. Terminal input would be
"./(program name) (filename).txt (filename2).txt" but this produces a segmentation fault (core dumped)
Whereas, if I type this in
"./(program name) (filename) (filename2) without the .txt file extension the code runs

Answer 1

If you put a debug statement as the first thing in your program printing the contents of argv[1] and argv[2] then you will be able to see the problem and we won't have to guess exactly what you are trying to do. It is very hard for us to understand this issue with a MCVE because you are opening files that exist on your computer but which might not exist on ours. So it could crash on your machine, but have some different error on mine.
"I skipped error checking" ... well that's fine when things work, but here something is going wrong: why not check the return codes and print out the error if there is one. For example:
#include <stdio.h>
#include <stdlib.h>
int main (int argc, char **argv){
FILE *inFile;
FILE *outFile;
if (argc < 3) {
fprintf("Only got %d arguments!\n", argc);
exit(1);
}
printf("arg1: %s, arg2: %s", argv[0], argv[1]);
inFile = fopen(argv[1], "r");
if (inFile == NULL) {
perror("Failed on in file: ");
exit(1);
}
outFile = fopen(argv[2], "w+");
if (outFile == NULL) {
perror("Failed on out file: ");
exit(1);
}
int ch = fgetc(inFile); /*as per comments this should be int */
while(ch != EOF){
fputc(ch, outFile);
ch = fgetc(inFile);
}
}

Answer 2

Nothing in your program should behave differently depending on the name of the input or output file.
But you don't check whether the fopen() calls succeeded.
I think what's happening is that the input file with the .txt extension simply doesn't exist. This causes fopen to fail, returning a null pointer, which you then assign to inFile. fgetc(inFile) then crashes.
Always check whether your calls succeeded or failed.
And as I mentioned in a comment, you need to assign the result of fgetc() to an int, not a char. It returns either a character value or the negative value EOF.
In addition you don't need two calls to fgetc, one before the loop and the other in the loop.
Suggested reading: section 12 of the comp.lang.c FAQ.