Question

I will use some CMD commands in my program and these commands might throw some exceptions. And as you know, when an exception accours, CMD writes its own error message the screen. But, I want to write my own error message.

My question is this: Is there a way to block CMD messages and write only my own error messages?

P.S. This is not a complex program. It executes CMD commands using System().

Example:

Let’s say, the user can rename and copy any files in the program. As you know, if the user does not enter file’s path properly, an error message is showed on the screen. And I want that this error message never appears on the screen. Only my own error message is showed.

Thank you!

Answer 1

It depends on your platform and the commands you are going to use. The usage of system() for calling console commands is by the way strongly discouraged by most people (it’s way to heavy for most purposes).
I would suggest to you using CreateProcess() with the CREATE_NO_WINDOW flag and waiting for the process to exit with a call to WaitForSingleObject() and GetExitCodeProcess().
This approach utilizes the fact, that most CMD command are executables, located somewhere in C:/Windows/....

/*
 * Executes a program and returns it's exit code.
 *
 * TODO: Error checking should be added for
 *   CreateProcess()
 *   WaitForSingleObject()
 *   GetExitCodeProcess()
 */
DWORD ExecCmdLine(TCHAR const* cmdline)
{
    STARTUPINFO si;
    memset(&si, 0, sizeof(si));
    si.cb = sizeof(si);
    PROCESS_INFORMATION pi;
    memset(&pi, 0, sizeof(pi));
    ::CreateProcess(NULL, cmdline, NULL, NULL, FALSE, CREATE_NO_WINDOW, NULL, NULL, &si, &pi);
    ::CloseHandle(pi.Thread);
    ::WaitForSingleObject(pi.hProcess, INFINITE);
    DWORD exitcode;
    ::GetExitCodeProcess(pi.hProcess, &exitcode);
    ::CloseHandle(pi.hProcess);
    return exitcode;
}

If you want to retrieve the output of the command you could also provide hStdOutput, hStdError in the STARTUPINFO structure and set STARTF_USESTDHANDLES in STARTUPINFO.dwFlags.
You can even do other things in your own program while the command is executing (especially as you mentioned file copy). This one is done the C++ way:

/*
 * TODO: Error checking should be added for
 *   CreateProcess()
 *   WaitForSingleObject()
 *   GetExitCodeProcess()
 */
class AsyncCmd
{
public:
    AsyncCmd(std::string const& cmdline)
        : cmdline(cmdline),
          processHandle(NULL)
    {
    }
    ~AsyncCmd()
    {
        if (this->processHandle != NULL)
            ::CloseHandle(this->processHandle);
    }
    // Starts the execution of the commandline.
    void Start(HANDLE hOut = GetStdHandle(STD_OUTPUT_HANDLE), HANDLE hErr = GetStdHandle(STD_ERROR_HANDLE))
    {
        STARTUPINFO si;
        memset(&si, 0, sizeof(si));
        si.cb = sizeof(si);
        si.dwFlags = STARTF_USESTDHANDLES;
        si.hStdInput = GetStdHandle(STD_INPUT_HANDLE);
        si.hStdOutput = hOut;
        si.hStdError = hErr;
        PROCESS_INFORMATION pi;
        memset(&pi, 0, sizeof(pi));
        ::CreateProcess(NULL, this->cmdline.c_str(), NULL, NULL, FALSE, CREATE_NO_WINDOW, NULL, NULL, &si, &pi);
        ::CloseHandle(pi.hThread);
        this->processHandle = pi.hProcess;
    }
    // Blocks until execution is finished and returns the exit code.
    DWORD ExitCode()
    {
        ::WaitForSingleObject(this->processHandle, INFINITE);
        DWORD exitcode;
        ::GetExitCodeProcess(this->processHandle, &exitcode);
        return exitcode;
    }
private:
    AsyncCmd(AsyncCmd const&);
    AsyncCmd& operator=(AsyncCmd const&);
    std::string cmdline;
    HANDLE processHandle;
}