Redirect both cout and stdout to a string in C++ for Unit Testing

Question

I\'m working on getting some legacy code under unit tests and sometimes the only way to sense an existing program behavior is from the console output.

I see lots of

Answer 1

You can use freopen(..., stdout) and then dump the file into memory or a std::string.

Answer 2

This may be an alternative:

char bigOutBuf[8192];
char savBuf[8192];

fflush(stdout);
setvbuf(stdout,bigOutBuf,IOFBF,8192);//stdout uses your buffer

//after each operation
strncpy(savBuf,bigOutBuf,8192);//won't flush until full or fflush called

//...

//at long last finished
setbuf(stdout,NULL);//reset to unnamed buffer

This just intercepts the buffered output, so still goes to console or wherever.

Hope this helps.

Answer 3

std::stringstream may be what you're looking for.

UPDATE
Alright, this is a bit of hack, but maybe you could do this to grab the printf output:

char huge_string_buf[MASSIVE_SIZE];
freopen("NUL", "a", stdout);
setbuf(stdout, huge_string_buffer);

Note you should use "/dev/null" for linux instead of "NUL". That will rapidly start to fill up huge_string_buffer. If you want to be able to continue redirecting output after the buffer is full you'll have to call fflush(), otherwise it will throw an error. See std::setbuf for more info.

Answer 4

Try sprintf, that's more efficient.

int i;
char str[] = "asdf";
char output[256];
sprintf(output, "asdfasdf %s %d\n", str, i);