how C output LF to stdout without being changed to

问题:

On Windows this

#include <stdio.h>

int main() { 
    putc('A',stdout);
    putc('\r',stdout); 
    putc('\n',stdout);
}

outputs

A<CR><CR><LF>

How to write just LF char to stdout without automatic conversion to CR LF?

I need it to make simple socket stream reader to stdout. I've tried bcc32 from CodeGear, mingw, tinycc all yield same result, changing putc to putchar, fputc, fwrite doesn't help either.

回答1:

The MSVC solution is:

#include <io.h>
#include <fcntl.h>
...
_setmode(1,_O_BINARY)

Other runtimes may provide the C99 solution or an alternate way. EDIT: I believe setmode([file number],O_BINARY) originated on Borland Turbo C, and other compilers for MS-DOS and Windows imitated it. The _ prefix is done to keep the namespace clean, and may not be present on some compilers.

回答2:

A text file converts the C character '\n' into the native line ending on output, and converts the native line ending on input into a single '\n'.

To get the result you require, you'd have to change stdout into a binary file stream.

A partial answer is found here. If you have a C99-compliant library, using:

if (freopen(0, "wb", stdout) == 0)
    ...oops...operation failed...

will attempt to change standard output to a binary stream. However, on Windows, the 'C99-compliant library' might be a problem. Nominally, this is the portable (because standard) answer. There is likely a Windows-specific function to do the same job.

回答3:

Just output LF character, like this: putc('\x0A', stdout)

回答4:

#ifdef _WIN32
#include <fcntl.h>
#include <io.h>
#endif

#ifdef __BORLANDC__
#define _setmode setmode
#endif

#include <stdio.h>

static void binary_stdout(void) {
#ifdef _WIN32
    _setmode(_fileno(stdout), _O_BINARY);
#endif
}

int main(void) {
    binary_stdout();
    printf("\n");
    return 0;
}