Difference between fprintf, printf and sprintf?

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.

printf outputs to the standard output stream (stdout)

fprintf goes to a file handle (FILE*)

sprintf goes to a buffer you allocated. (char*)

printf("format", args) is used to print the data onto the standard output which is often a computer monitor.

sprintf(char *, "format", args) is like printf. Instead of displaying the formated string on the standard output i.e. a monitor, it stores the formated data in a string pointed to by the char pointer (the very first parameter). The string location is the only difference between printf and sprint syntax.

fprintf(FILE *fp, "format", args) is like printf again. Here, instead of displaying the data on the monitor, or saving it in some string, the formatted data is saved on a file which is pointed to by the file pointer which is used as the first parameter to fprintf. The file pointer is the only addition to the syntax of printf.

If stdout file is used as the first parameter in fprintf, its working is then considered equivalent to that of printf.