How to handle newline character '\n' in any text file against the linux newline characters \r\n characters?

Question

I have a C code which reads 1 line at a time, from a file opened in text mode using

fgets(buf,200,fin); 

The input file which fgets() reads lines from, is an command line argument to the program.

Now fgets leaves the newline character included in the string copied to buf.

Somewhere do the line in the code I check

length = strlen(buf);

For some input files , which I guess are edited in *nix environment newline character is just '\n'

But for some other test case input files(which I guess are edited/created under Windows environment) have 2 characters indicating a newline - '\r''\n'

I want to remove the newline character and want to put a '\0' as the string terminator character. So I have to either do -

    if(len == (N+1))
    {
    if(buf[length-1] == '\n')
     {
         buf[length-2] = '\0'; //for a `\r\n` newline
     }
    } 

or

if(len == (N))
{
 if(buf[length-1] == '\n')
 {
     buf[length-1] = '\0'; //for a `\n` newline
 }
} 

Since the text files are passed as commandline argument to the program I have no control of how it is edited/composed and hence cannot filter it using some tool to make newlines consistent.

How can I handle this situation?

Is there any fgets equivalent function in standard C library(no extensions) which can handle these inconsistent newline characters and return a string without them?

Answer 1

I like to update length at the same time

if (buf[length - 1] == '\n') buf[--length] = 0;
if (buf[length - 1] == '\r') buf[--length] = 0;

or, to remove all trailing whitespace

/* remember to #include <ctype.h> */
while ((length > 0) && isspace((unsigned char)buf[length - 1])) {
    buf[--length] = 0;
}