Unexpected behaviour when removing inline comments in C - c

Question

Stack Overflow! I am on my learning process with the C technology. I have a function which gets an input file, seeks through the file and writes the contents to the output file without the comments.
The function works but it also brakes at some cases.
My Function:
void removeComments(char* input, char* output)
{
FILE* in = fopen(input,"r");
FILE* out = fopen(ouput,"w");
char c;
while((c = fgetc(in)) != EOF)
{
if(c == '/')
{
c = fgetc(in);
if(c == '/')
{
while((c = fgetc(in)) != '\n');
}
else
{
fputc('/', out);
}
}
else
{
fputc(c,out);
}
}
fclose(in);
fclose(out);
}
But when I give a file like this as input:
// Parameters: a, the first integer; b the second integer.
// Returns: the sum.
int add(int a, int b)
{
return a + b; // An inline comment.
}
int sample = sample;
When removing the inline comment it fails to reach the '\n' for some reason and it gives output:
int add(int a, int b)
{
return a + b; }
int sample = sample;
[EDIT]
Thanks for helping me! It works with the case I posted but it brakes in another.
Current code:
FILE* in = fopen(input,"r");
FILE* out = fopen(output,"w");
if (in == NULL) {
printf("cannot read %s\n", input);
return; /* change signature to return 0 ? */
}
if (out == NULL) {
printf("cannot write in %s\n", output);
return; /* change signature to return 0 ? */
}
int c;
int startline = 1;
while((c = fgetc(in)) != EOF)
{
if(c == '/')
{
c = fgetc(in);
if(c == '/')
{
while((c = fgetc(in)) != '\n')
{
if (c == EOF) {
fclose(in);
fclose(out);
return; /* change signature to return 1 ? */
}
}
if (! startline)
fputc('\n', out);
startline = 1;
}
else if (c == EOF)
break;
else {
fputc('/', out);
startline = 0;
}
}
else
{
fputc(c,out);
startline = (c == '\n');
}
}
fclose(in);
fclose(out);
When the file contains division the second variable disappears.
Example:
int divide(int a, int b)
{
return a/b;
}
It gives back:
int divide(int a, int b)
{
return a/;
}

Answer 1

after
while((c = fgetc(in)) != '\n');
you need a fputc('\n', out);
Additional remarks :
In
char c;
while((c = fgetc(in)) != EOF)
c must be an int to manage EOF
Just a typo : ouput must be output to compile
You do not manages well the EOF after you read a '/'
You missed to check the result of the fopen
A proposal :
#include <stdio.h>
void removeComments(char* input, char* output)
{
FILE* in = fopen(input,"r");
FILE* out = fopen(output,"w");
if (in == NULL) {
printf("cannot read %s\n", input);
return; /* change signature to return 0 ? */
}
if (out == NULL) {
printf("cannot write in %s\n", output);
return; /* change signature to return 0 ? */
}
int c;
while((c = fgetc(in)) != EOF)
{
if(c == '/')
{
c = fgetc(in);
if(c == '/')
{
while((c = fgetc(in)) != '\n')
{
if (c == EOF) {
fclose(in);
fclose(out);
return; /* change signature to return 1 ? */
}
}
fputc('\n', out);
}
else if (c == EOF) {
fputc('/', out);
break;
}
else
fputc('/', out);
fputc(c, out);
}
else
{
fputc(c,out);
}
}
fclose(in);
fclose(out);
/* change signature to return 1 ? */
}
int main(int argc, char ** argv)
{
removeComments(argv[1], argv[2]);
}
As Tormund Giantsbane says in a remark it is better to completely remove the line containing only a comment (comment starting on the first column), that new proposal does that :
#include <stdio.h>
void removeComments(char* input, char* output)
{
FILE* in = fopen(input,"r");
FILE* out = fopen(output,"w");
if (in == NULL) {
printf("cannot read %s\n", input);
return; /* change signature to return 0 ? */
}
if (out == NULL) {
printf("cannot write in %s\n", output);
return; /* change signature to return 0 ? */
}
int c;
int startline = 1;
while((c = fgetc(in)) != EOF)
{
if(c == '/')
{
c = fgetc(in);
if(c == '/')
{
while((c = fgetc(in)) != '\n')
{
if (c == EOF) {
fclose(in);
fclose(out);
return; /* change signature to return 1 ? */
}
}
if (! startline)
fputc('\n', out);
startline = 1;
}
else if (c == EOF) {
fputc('/', out);
break;
}
else {
fputc('/', out);
fputc(c, out);
startline = 0;
}
}
else
{
fputc(c,out);
startline = (c == '\n');
}
}
fclose(in);
fclose(out);
/* change signature to return 1 ? */
}
int main(int argc, char ** argv)
{
removeComments(argv[1], argv[2]);
}
Compilation and execution :
pi#raspberrypi:/tmp $ gcc -pedantic -Wextra -g r.c
pi#raspberrypi:/tmp $ cat i
// Parameters: a, the first integer; b the second integer.
// Returns: the sum.
int add(int a, int b)
{
return a + b/c; // An inline comment.
}
int sample = sample;
pi#raspberrypi:/tmp $ ./a.out i o
pi#raspberrypi:/tmp $ cat o
int add(int a, int b)
{
return a + b/c;
}
int sample = sample;
As said by DavidC. in a remark if // is placed in a string the result will not be the expected one, it is also the case in a character even illegal (I mean '//' must not be changed), what about the C comments (/* .. // ... */) etc

Answer 2

When removing the inline comment it fails to reach the '\n' for some reason
Well no, if it failed to reach or see the newline at the end of an inline comment then the program would, presumably, consume the entire rest of the file. What it actually fails to do is write such newlines to the output.
Consider your comment-eating code:
while((c = fgetc(in)) != '\n');
That loop terminates when a newline is read. At that point, the newline, having already been read, is not available to be read from the input again, so your general read / write provisions will not handle it. If you want the such newlines to be preserved, then you need to print them in the comment-handling branch.
Additional notes:
fgetc returns an int, not a char, and you need to handle it as such in order to be able to correctly detect end-of-file.
Your program will go into an infinite loop if the input ends with an inline comment that is not terminated by a newline. Such source is technically non-conforming, but even so, you ought to handle it.