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

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 examples online for how to redirect stdout to another file in C++, but is there a way I can redirect it to an in-memory stream so my tests don't have to rely on the disk?

I'd like to get anything that the legacy code sends to stdout into a std::string so I can easily .find on the output.

Edit

The legacy code is so bad that it users a mixture of cout << .. and printf. Here is what I have so far:

void TestSuite::setUp(void)
{
    oldStdoutBuf = std::cout.rdbuf();
    std::cout.rdbuf(consoleOutput.rdbuf());
}
void TestSuite::tearDown(void)
{
    std::cout.rdbuf(oldStdoutBuf);
}

The problem is that this does not capture output using printf. I would like something that gets both. Any ideas?

like image 324
thelsdj Avatar asked Jul 21 '09 22:07

thelsdj


3 Answers

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.

like image 120
Gabe Avatar answered Nov 05 '22 21:11

Gabe


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

like image 31
MSN Avatar answered Nov 05 '22 23:11

MSN


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.

like image 2
cvsdave Avatar answered Nov 05 '22 21:11

cvsdave