Question

I am using CreateProcess to invoke cl to compile and link another C++ program (TestProg.cxx) into a DLL. I invoke cl.exe with the following compilation options:

compilation options:

/Od /nologo /Fo /RTC /w /Zc TestProg.cxx /DLL

the call:

if ( CreateProcess(PATH_TO_EXE, COMPILATION_OPTIONS, NULL,NULL,
                   FALSE,0,NULL,NULL,&si,&pi) ) 
{
    //....
}

If TestProg.exe contains #include <iostream.h> I got the following compilation error:

TestProg.cpp(1) : fatal error C1034: iostream.h: no include path set

Without any #include command, I got the following linkage error:

LINK : fatal error LNK1104: cannot open file 'LIBCMT.lib'

What am I doing wrong?

I searched the answer for the last 6-7 hours on the web, but didn’t find it. Using windows API is new to me.

Answer 1

If you look at the definition of CreateProcess:

BOOL WINAPI CreateProcess(
  __in_opt     LPCTSTR lpApplicationName,
  __inout_opt  LPTSTR lpCommandLine,
  __in_opt     LPSECURITY_ATTRIBUTES lpProcessAttributes,
  __in_opt     LPSECURITY_ATTRIBUTES lpThreadAttributes,
  __in         BOOL bInheritHandles,
  __in         DWORD dwCreationFlags,
  __in_opt     LPVOID lpEnvironment,
  __in_opt     LPCTSTR lpCurrentDirectory,
  __in         LPSTARTUPINFO lpStartupInfo,
  __out        LPPROCESS_INFORMATION lpProcessInformation
);

You’re setting the optional parameter __in_opt LPVOID lpEnvironment, to NULL.

According to said definition:

A pointer to the environment block for the new process. If this parameter is NULL, the new process uses the environment of the calling process.

cl.exe gets its include location information and library search paths from environment variables – have a look at setenv.bat in the VS directory. In this case, neither your calling process or your target process are running in an environment where these variables are set.

You have a choice – you can create the environment variables yourself according to the MSDN:

An environment block consists of a null-terminated block of
null-terminated strings. Each string is in the following form:

name=value\0

Because the equal sign is used as a separator, it must not be used in
the name of an environment variable.

Or you can require your program to be run from the VS tools prompt. A good check this is actually the problem would be to run your program from this prompt, rather than Visual Studio, to see if that fixes the issue.

The reason not using #include produces a linker error is due to the fact if there are no includes, cl.exe won’t look for them – it then looks for the C/C++ runtime libs.

As a side note – I believe the standard in C++ is to #include <iostream> i.e without the .h.