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Asked: 2026-05-11T04:16:52+00:00

I’ve coded a program in C that sends messages to the stdout using printf

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I’ve coded a program in C that sends messages to the stdout using printf and I’m having trouble redirecting the output to a file (running from bash).

I’ve tried:

./program argument >> program.out ./program argument > program.out ./program >> program.out argument ./program > program.out argument

In each case, the file program.out is created but it remains empty. After the execution ends the file size is 0.

If I omit the redirection when executing the program:

./program argument

Then, all messages sent to stdout using printf are shown in the terminal.

I have other C programs for which I’ve no problem redirecting the output this way. Does it have to do with the program itself? with the argument passing? Where should look for the problem?

Some details about the C program:

  • It does not read anything from stdin
  • It uses BSD Internet Domain sockets
  • It uses POSIX threads
  • It assigns a special handler function for SIGINT signal using sigaction
  • It sends lots of newlines to stdout (for those of you thinking I should flush)

Some code:

int main(int argc, char** argv) {     printf('Execution started\n');     do     {                 /* lots of printf here */     } while (1);     /* Code never reached */     pthread_exit(EXIT_SUCCESS); }
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1 Answer

  1. Flushing after newlines only works when printing to a terminal, but not necessarily when printing to a file. A quick Google search revealed this page with further information: http://www.pixelbeat.org/programming/stdio_buffering/

    See the section titled ‘Default Buffering modes’.

    You might have to add some calls to fflush(stdout), after all.

    You could also set the buffer size and behavior using setvbuf.

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