C++ Windows Pipe Writefile to a Variable? - c++

Question

I used the "Creating a Child Process with Redirected Input and Output" tutorial from msdn.
Link: https://msdn.microsoft.com/en-us/library/windows/desktop/ms682499(v=vs.85).aspx
Everything works fine the parent process display it totally correct. But instead of Reading it from the pipe and write it to the Parent STD_OUTPUT_HANDLE I want to read from the pipe and write the output in a variable type.
Here is what I mean:
void ReadFromPipe(void)
// Read output from the child process's pipe for STDOUT
// and write to the parent process's pipe for STDOUT.
// Stop when there is no more data.
{
DWORD dwRead, dwWritten;
CHAR chBuf[BUFSIZE];
BOOL bSuccess = FALSE;
HANDLE hParentStdOut = GetStdHandle(STD_OUTPUT_HANDLE);
for (;;)
{
bSuccess = ReadFile( g_hChildStd_OUT_Rd, chBuf, BUFSIZE, &dwRead, NULL);
if( ! bSuccess || dwRead == 0 ) break;
bSuccess = WriteFile(hParentStdOut, chBuf,
dwRead, &dwWritten, NULL);
if (! bSuccess ) break;
}
}
I managed to get the chBuf after the Writefile function and tried to build a string out of it but it contains duplicates and characters which I dont want to have in my string. So my string contains of a lot more characters than the parent console output.
My workaround is that I save the output to a file and then stream it to a variable but that solution sucks because if you run two instances of my app I have to manage this to dont overwrite each other file and so on it getting more and more complicated that I would like a cleaner solution
Can you help me on this?

Answer 1

I managed to get the chBuf after the Writefile function and tried to build a string out of it but it contains duplicates and characters which I dont want to have in my string. So my string contains of a lot more characters than the parent console output.
Most probably, you are building your string disregarding dwRead - i.e., you always assume that the full buffer has been read - or something like that. Still, building an std::string out of the data you are reading is actually quite simple:
std::string ReadFromPipe(void) {
std::string ret;
DWORD dwRead;
CHAR chBuf[BUFSIZE];
BOOL bSuccess = FALSE;
for (;;) {
bSuccess = ReadFile( g_hChildStd_OUT_Rd, chBuf, BUFSIZE, &dwRead, NULL);
if( ! bSuccess || dwRead == 0 ) break;
ret.append(chBuf, dwRead);
}
return ret;
}