Difference between fprintf, printf and sprintf?

c io stream printf
Vishwanath Dalvi picture Vishwanath Dalvi · Jan 7, 2011 · Viewed 219.3k times · Source

Can anyone explain in simple English about the differences between printf, fprintf, and sprintf with examples?

What stream is it in?

I'm really confused between the three of these while reading about "File Handling in C".

Answer

John Bode picture John Bode · Jan 7, 2011

In C, a "stream" is an abstraction; from the program's perspective it is simply a producer (input stream) or consumer (output stream) of bytes. It can correspond to a file on disk, to a pipe, to your terminal, or to some other device such as a printer or tty. The FILE type contains information about the stream. Normally, you don't mess with a FILE object's contents directly, you just pass a pointer to it to the various I/O routines.

There are three standard streams: stdin is a pointer to the standard input stream, stdout is a pointer to the standard output stream, and stderr is a pointer to the standard error output stream. In an interactive session, the three usually refer to your console, although you can redirect them to point to other files or devices:

$ myprog < inputfile.dat > output.txt 2> errors.txt

In this example, stdin now points to inputfile.dat, stdout points to output.txt, and stderr points to errors.txt.

fprintf writes formatted text to the output stream you specify.

printf is equivalent to writing fprintf(stdout, ...) and writes formatted text to wherever the standard output stream is currently pointing.

sprintf writes formatted text to an array of char, as opposed to a stream.

Related questions

Read from file or stdin

I am writing a utility which accepts either a filename, or reads from stdin. I would like to know the most robust / fastest way of checking to see if stdin exists (data is being piped to the program) and if …

Read More
How to read a line from the console in C?

What is the simplest way to read a full line in a C console program The text entered might have a variable length and we can't make any assumption about its content.

Read More
How to prevent SIGPIPEs (or handle them properly)

I have a small server program that accepts connections on a TCP or local UNIX socket, reads a simple command and (depending on the command) sends a reply. The problem is that the client may have no interest in the …

Read More