windows cmd works via WinExec but not via popen

Question

Why does the following code work via WinExec(), but not via popen()? It should do the same, right?

std::string command = "C:\\Windows\\system32\\cmd.exe /c \" cd /D \"C:\\Users\\Johannes\\Desktop\\test\" && xcopy /I .\\data\\*.* .\\build\\ \"";

WinExec(command.c_str(), SW_HIDE); //working

FILE *pipe = popen(command.c_str(), "r"); //NOT working

After some testing I'm even more confused, because some commands like mkdir work but not with xcopy:

1:

// not working
popen("C:\\Windows\\system32\\cmd.exe /c \" cd \"C:\\Users\\Johannes\\Desktop\\test\" && xcopy .\\data\\*.* .\\build\\ \"", "r");

2:

// working
popen("C:\\Windows\\system32\\cmd.exe /c \" cd \"C:\\Users\\Johannes\\Desktop\\test\" && mkdir test2 \"", "r");

3:

// not working 
popen("C:\\Windows\\system32\\cmd.exe /c \" cd \"C:\\Users\\Johannes\\Desktop\\test\" && xcopy \"C:\\Users\\Johannes\\Desktop\\test\\data\\*.*\" \"C:\\Users\\Johannes\\Desktop\\test\\build\\\" \"", "r");

4:

// working 
popen("C:\\Windows\\system32\\cmd.exe /c \" xcopy \"C:\\Users\\Johannes\\Desktop\\test\\data\\*.*\" \"C:\\Users\\Johannes\\Desktop\\test\\build\\\" \"", "r");

Answer 1

From the documentation (emphasis mine):

The _popen function creates a pipe. It then asynchronously executes a spawned copy of the command processor, and uses command as the command line.

So I think you should omit the cmd /c part and that should make it easier to get it to work.

Answer 2

I found a solution. If I do the following it works:

std::string command = "start cmd /c \" cd /D \"C:\\Users\\Johannes\\Desktop\\test\" && xcopy /I /E /C /Y .\\data\\*.* .\\build\\ \"";

or

std::string command = "cmd /c \" cd /D \"C:\\Users\\Johannes\\Desktop\\test\" && start xcopy /I /E /C /Y .\\data\\*.* .\\build\\ \"";.

From now on I will always do start cmd /c "", then it will always work in any case.

But one question remains. Why does it work like this and not otherwise?