winApi create process using c++

Question

I'm trying to open a picture using WinApi in c++, tried both createProcessW and createProcessA, my main problem was concatenating the strings that are used as cmdLine parameter. this is what iv'e got:

STARTUPINFOW process_startup_info{ 0 };
process_startup_info.cb = sizeof(process_startup_info); // setup size of strcture in bytes

PROCESS_INFORMATION process_info{ 0 };

wchar_t* s = L"\"C:\\Windows\\system32\\mspaint.exe\" ";
std::string s2 = pic.getPath();
// connecting strings here
if (CreateProcessW(NULL, /* string should be here */, NULL, NULL, TRUE, 0, NULL, NULL, &process_startup_info, &process_info))
{
    WaitForSingleObject(process_info.hProcess, INFINITE);
    CloseHandle(process_info.hProcess);
    CloseHandle(process_info.hThread);
}

You need to convert the path to the picture to a wide string before you can concatenate the two. — Ted Lyngmo
– Ted Lyngmo, Commented Mar 24, 2020 at 18:09

NTDLS · Accepted Answer · 2020-03-24 19:25:44Z

3

Try to use the same types everywhere for the command and the params if you can. Here I am using a wstring, concatenating a parameter to the command then casting it to LPWSTR for the CreateProcess method.

STARTUPINFOW process_startup_info{ 0 };
process_startup_info.cb = sizeof(process_startup_info); // setup size of strcture in bytes

PROCESS_INFORMATION process_info{ 0 };

std::wstring params = L"\"C:\\Windows\\system32\\mspaint.exe\" ";
params.append(L"\"C:\\Vroom Owl.png\"");

// connecting strings here
if (CreateProcessW(NULL, (LPWSTR)params.data(), NULL, NULL, TRUE, 0, NULL, NULL, &process_startup_info, &process_info))
{
    WaitForSingleObject(process_info.hProcess, INFINITE);
    CloseHandle(process_info.hProcess);
    CloseHandle(process_info.hThread);
}

edited Mar 24, 2020 at 19:25

answered Mar 24, 2020 at 18:15

NTDLS

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3 Comments

Remy Lebeau Over a year ago

Setting the project to multi-byte instead of Unicode will make CreateProcess() call CreateProcessA() instead of CreateProcessW(). It is actually better NOT to rely on the TCHAR macros. In this case, if you use std::wstring then you should call CreateProcessW() directly to match. Also note that using const_cast<LPWSTR>(params.c_str()) is technically undefined behavior, use params.data() (C++17 or later) or &params[0] (C++11 or later) instead (std::(w)string data was not guaranteed to be stored in sequential memory prior to C++11, but it usually was in practice).

NTDLS Over a year ago

@RemyLebeau I can get on board with that. I'll update my answer accordingly.

Remy Lebeau Over a year ago

Don't cast away const-ness if you can help it. If your compiler has a data() method available but not a non-const version of it, using &[0] will work and no cast needed of it.

Landstalker · Accepted Answer · 2020-03-24 18:49:03Z

0

In include :

#include <sstream>

In code:

std::wstringstream wstringCmd;

std::wstring wstrExec = L"\"C:\\Windows\\system32\\mspaint.exe\" "; //<- wstring 
std::string strPic = pic.getPath(); //<- if getPath() return char  
// std::wstring wstrPic = pic.getPath();//<- if getPath() return wchar  

// you can combine as you like ...
wstringCmd << wstrExec.c_str() << strPic.c_str(); // or << wstrPic.c_str();
std::wstring wstrCommande= wstringCmd.str();

edited Mar 24, 2020 at 18:49

answered Mar 24, 2020 at 18:12

Landstalker

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6 Comments

NTDLS Over a year ago

I'm confused by the strPic and wstrPic values here. The method calls are enclosed in double quotes. Surely that was an oversight.

Remy Lebeau Over a year ago

Also, you can't stream a std::string or char* into a std::wstringstream, either. You would have to convert the std::string to std::wstring first

Landstalker Over a year ago

@NTDLS it was just to explain that we have "string" or L"string"

Landstalker Over a year ago

@RemyLebeau try it, if it doesn't work, we'll talk about it again

Remy Lebeau Over a year ago

@Landstalker I did try it, and OK granted, << works for char* even when the stream is std::wstringstream, but it does not work for std::string. Also, you can't save a std::wstring from std::wstringstream.str() to a std::string.

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