Updating the PATH environment variable in Windows using C++ - c++

Question

I am trying to launch a new process from my current process. I am using CreateProcess() to launch it. The issue is that I need to have certain directories in my PATH to successfully do so. Here is my current implementation but it doesn't work. What am I doing wrong?
// Environment variables
char *env = new char[2048];
char *ptr = env;
char temp[MAX_PATH] = "PATH=";
strcpy(ptr, strcat(temp, plugin_path));
ptr += strlen(ptr) + 1;
char temp2[MAX_PATH] = "PATH=";
strcpy(ptr, strcat(temp, lib_path));
ptr += strlen(ptr) + 1;
*ptr = '\0';
// Execute
STARTUPINFO si;
PROCESS_INFORMATION pi;
ZeroMemory(&si, sizeof(si));
si.cb = sizeof(si);
ZeroMemory(&pi, sizeof(pi));
// error checking required
if(!CreateProcess(
NULL, // application name
command_path, // app.exe
NULL,
NULL,
TRUE,
0,
env, // environment
NULL,
&si,
&pi)) {
std::cout << GetLastError();
return 1;
}
WaitForSingleObject(pi.hProcess, INFINITE);
CloseHandle(pi.hProcess);
CloseHandle(pi.hThread);
std::cout << "Process Started!";
Please let me know if anything else is required.
EDIT: Somebody mentioned below that I need to be a little more specific. It doesn't work in the sense that the environment variables don't get passed. It fails because the library path is not in PATH. The createProcess does actually launch it though.
EDIT2: Here's the updated code. Same problem. Further, CreateProcess throws error 1087 which doesn't seem to exist in the docs.
// Environment variables
char env[2048];
char *ptr = env;
char *path_path = getenv("PATH");
// copy original path
memcpy(ptr, path_path, strlen(path_path));
ptr += strlen(ptr) + 1;
memcpy(ptr, ";", 1);
ptr++;
// copy plugin path
memcpy(ptr, plugin_path, strlen(plugin_path));
ptr += strlen(plugin_path) + 1;
memcpy(ptr, ";", 1);
ptr++;
// copy libpath
memcpy(ptr, lib_path, strlen(lib_path));
ptr += strlen(lib_path) + 1;
memcpy(ptr, ";", 1);
ptr++;
// double null terminated
memcpy(ptr, "\0\0", 2);
std::cout << "ENV : " << env << std::endl;
// error checking required
if(!CreateProcess(
NULL, // application name
command_path, // app.exe
NULL,
NULL,
TRUE,
0,
env, // environment
NULL,
&si,
&pi)) {
std::cout << GetLastError();
return 1;
}
WaitForSingleObject(pi.hProcess, INFINITE);
CloseHandle(pi.hProcess);
CloseHandle(pi.hThread);
std::cout << "Process Started!";

Answer 1

The PATH variable is a single variable. Different directories are listed in that variable, separated by semi-colons. But you've attempted to define the variable twice. That is the mistake.
The code should be something like this (assuming that you want to extend the existing path):
char *env = new char[2048]; // fingers crossed this is enough
strcpy(env, "PATH=");
strcat(env, getenv("PATH"));
strcat(env, ";");
strcat(env, plugin_path);
strcat(env, ";");
strcat(env, lib_path);
env[strlen(env)+1] = '\0';
Although this code (as is yours in the question) is simply begging for a buffer overrun.
It would be so much easier if you used C++ facilities to build your strings. For instance:
std::stringstream ss;
ss << "PATH=" << getenv("PATH");
ss << ";" << plugin_path;
ss << ";" << lib_path;
ss << '\0';
std::string env = ss.str();
Then pass env.c_str() to CreateProcess.
Not only does this make the code easier to read and verify, you know that you won't overrun any buffers.
I also note that you are passing an environment that has only one variable defined in it, namely PATH. It might be better if you started from the environment of the calling process, added the extra directories to PATH, and then passed that as the environment for the new process.

Answer 2

#include <iostream>
#include <windows.h>
#include <cstring>
#include "tchar.h"
void SetUserVariablePath(){
HKEY hkey;
long regOpenResult;
const char key_name[] = "Environment";
const char path[]="D:/custom_command"; //new_value path need to update
regOpenResult = RegOpenKeyEx(HKEY_CURRENT_USER,key_name, 0, KEY_ALL_ACCESS, &hkey);
LPCSTR stuff = "VVS_LOGGING_PATH"; //Variable Name
RegSetValueEx(hkey,stuff,0,REG_SZ,(BYTE*) path, strlen(path));
RegCloseKey(hkey);
}
void GetUserVariablePath(){
static const char path[] = "VVS_LOGGING_PATH" ; //Variable Name
static BYTE buffer1[1000000] ;
DWORD buffsz1 = sizeof(buffer1) ;
{
//HKEY_CURRENT_USER\Environment
const char key_name[] = "Environment";
HKEY key ;
if( RegOpenKeyExA( HKEY_CURRENT_USER, key_name, 0, KEY_QUERY_VALUE, std::addressof(key) ) == 0 &&
RegQueryValueExA( key, path, nullptr, nullptr, buffer1, std::addressof(buffsz1) ) == 0 )
{
std::cout << "The updated value of the user variable is : " << reinterpret_cast<const char*>(buffer1) << '\n' ;
}
}
}
int main()
{
SetUserVariablePath();
GetUserVariablePath();
return 0;
}