Question

I am using C++ in Ubuntu with codeBlocks, boost 1.46 in GCC 4.7 [ yield_k.hpp ]

I get this compile time error:

error : Sleep was not declared in this scope

Code:

#include <iostream>
using namespace std;
int main() { 
  cout << "nitrate";
  cout << flush;
  sleep(1000);
  cout << "firtilizers";
  return 0;
}

How do I resolve this error? I want the program to hang for 1 second.

Answer 1

Sleep is a Windows function.

For Unix, look into using nanosleep (POSIX) or usleep (BSD; deprecated).

A nanosleep example:

void my_sleep(unsigned msec) {
    struct timespec req, rem;
    int err;
    req.tv_sec = msec / 1000;
    req.tv_nsec = (msec % 1000) * 1000000;
    while ((req.tv_sec != 0) || (req.tv_nsec != 0)) {
        if (nanosleep(&req, &rem) == 0)
            break;
        err = errno;
        // Interrupted; continue
        if (err == EINTR) {
            req.tv_sec = rem.tv_sec;
            req.tv_nsec = rem.tv_nsec;
        }
        // Unhandleable error (EFAULT (bad pointer), EINVAL (bad timeval in tv_nsec), or ENOSYS (function not supported))
        break;
    }
}

You will need <time.h> and <errno.h>, available in C++ as <ctime> and <cerrno>.

usleep is simpler to use (just multiply by 1000, so make it an inline function). However, it’s impossible to guarantee that that sleeping will occur for a given amount of time, it’s deprecated, and you need to extern "C" { }-include <unistd.h>.

A third choice is to use select and struct timeval, as seen in http://source.winehq.org/git/wine.git/blob/HEAD:/dlls/ntdll/sync.c#l1204 (this is how wine emulates Sleep, which itself is just a wrapper for SleepEx).

Note: sleep (lowercase ‘s’), whose declaration is in <unistd.h>, is not an acceptable substitute, since its granularity is seconds, coarser than that of Windows’ Sleep (uppercase ‘s’), which has a granularity of milliseconds.

Regarding your second error, ___XXXcall is a MSVC++-specific token (as are __dllXXX, __naked, __inline, etc.). If you really need stdcall, use __attribute__((stdcall)) or similar to emulate it in gcc.

Note: unless your compile target is a Windows binary and you’re using Win32 APIs, use of or a requirement for stdcall is A Bad Sign™.