The Windows Processes and Threads 21

 

 

Changing Environment Variables Program Examples

 

Each process has an environment block associated with it. The environment block consists of a null-terminated block of null-terminated strings (meaning there are two null bytes at the end of the block), where each string is in the form:

 

name=value

 

All strings in the environment block must be sorted alphabetically by name. The sort is case-insensitive, Unicode order, without regard to locale. Because the equal sign is a separator, it must not be used in the name of an environment variable.

 

 

 

Environment Variables: Example 1

 

By default, a child process inherits a copy of the environment block of the parent process. The following example demonstrates how to create a new environment block to pass to a child process using CreateProcess(). This example uses the code in example three as the child process, EnvironVar3.exe. In this case you should try the third example first.

Create a new empty Win32 console application project. Give a suitable project name and change the project location if needed.

 

 

Then, add the source file and give it a suitable name.

 

 

 

Next, add the following source code.

 

#include <windows.h>

#include <tchar.h>

#include <stdio.h>

#include <strsafe.h>

 

#define BUFSIZE 4096

 

int wmain(int argc, WCHAR **argv)

{

    LPTSTR lpszCurrentVariable;

    // Child process to be executed

    WCHAR szAppName[]=L\\\\?\\C:\\amad\\EnvironVar3\\Debug\\EnvironVar3.exe;

    // WCHAR szAppName[]=L\\\\?\\C:\\WINDOWS\\system32\\sol.exe;

    STARTUPINFO si = {0};

    PROCESS_INFORMATION pi = {0};

    BOOL fSuccess;

    DWORD Ret = 100;

    LPTSTR lpszVariable;

    LPWCH lpvEnv;

     

    // Get the current process and thread IDs

    wprintf(LParent process ID (wmain()) is %u\n, GetCurrentProcessId());

    wprintf(LParent thread ID (wmain()) is %u\n, GetCurrentThreadId());

 

    // Get a pointer to the environment block

    lpvEnv = GetEnvironmentStrings();

 

    // If the returned pointer is NULL, exit

    if (lpvEnv == NULL)

    {

        wprintf(LGetEnvironmentStrings failed, error %d\n, GetLastError());

        return 1;

    }

      else

            wprintf(LGetEnvironmentStrings() is OK!\n);

 

    // Copy environment strings into an environment block

    lpszCurrentVariable = lpvEnv;

     

      // Frees a block of environment strings

    if(FreeEnvironmentStrings(lpvEnv) != 0)

            wprintf(L\nFreeEnvironmentStrings() - a block of environment strings was freed!\n);

      else

            wprintf(L\nFreeEnvironmentStrings() failed, error %u\n, GetLastError());

 

 

    if (FAILED(StringCchCopy(lpszCurrentVariable, BUFSIZE, LMyNewEnvSetting=awek gedik)))

    {

        wprintf(LStringCchCopy() - String copy failed\n);

        return 1;

    }

      else

            wprintf(LStringCchCopy() - env var was  copied successfully!\n);

 

    lpszCurrentVariable += lstrlen(lpszCurrentVariable) + 1;

    if (FAILED(StringCchCopy(lpszCurrentVariable, BUFSIZE, LMyNewVersion=2.34)))

    {

        wprintf(LStringCchCopy() - String copy failed\n);

        return 1;

    }

      else

            wprintf(LStringCchCopy() - Another env var was  copied successfully!\n);

 

    // Terminate the block with a NULL byte

    // Variable strings are separated by NULL byte, and the block is

    // terminated by a NULL byte

    lpszCurrentVariable += lstrlen(lpszCurrentVariable) + 1;

    *lpszCurrentVariable = (WCHAR)0;

 

    // Create the child process, specifying a new environment block

    SecureZeroMemory(&si, sizeof(STARTUPINFO));

    si.cb = sizeof(STARTUPINFO);

 

    fSuccess = CreateProcess(szAppName, NULL, NULL, NULL, TRUE, NULL,

        (LPVOID)lpszCurrentVariable,   // new environment block

        NULL, &si, &pi);

 

      // Validate

    if(!fSuccess)

    {

        wprintf(LCreateProcess() failed, error %d\n, GetLastError());

        return 1;

    }

      else

      {

            wprintf(L\nCreateProcess() - Child process was created successfully!\n);

            wprintf(LChild process ID is %u\n, pi.dwProcessId);

            wprintf(LChild thread ID is %u\n, pi.dwThreadId);

           

            // Verify the current process environment variable

            wprintf(L\n);

            system(set);

            wprintf(L\n);

      }

 

    // Get the current env var

    lpszVariable = GetEnvironmentStrings();

 

    // If the returned pointer is NULL, exit

    if (lpszVariable == NULL)

    {

        wprintf(LGetEnvironmentStrings() failed, error %d\n, GetLastError());

        return 1;

    }

      else

            wprintf(LGetEnvironmentStrings() is OK!\n);

 

    // Try to print it

    while(*lpszVariable)

    {

        wprintf(L%s\n, lpszVariable);

        lpszVariable += lstrlen(lpszVariable) + 1;

    }

 

    // Frees a block of environment strings

    if(FreeEnvironmentStrings(lpszVariable) != 0)

            wprintf(L\nFreeEnvironmentStrings() - a block of environment strings was freed!\n);

      else

            wprintf(L\nFreeEnvironmentStrings() failed, error %u\n, GetLastError());

 

    // Wait for the object to signal

    Ret = WaitForSingleObject(pi.hProcess, INFINITE);

      wprintf(L\nThe WaitForSingleObject return value is 0X%.8X\n, Ret);

     

    // Close process and thread handles.

    if(CloseHandle(pi.hProcess) != 0)

            wprintf(Lpi.hProcess handle was closed successfully!\n);

      else

            wprintf(LFailed to close pi.hProcess handle, error %u\n, GetLastError());

   

      if(CloseHandle(pi.hThread) != 0)

            wprintf(Lpi.hThread handle was closed successfully!\n);

      else

            wprintf(LFailed to close pi.hThread handle, error %u\n, GetLastError());

 

    return 0;

}

 

The following Application error displayed, however the output is consistent. The bug already solved for execve() or the wexecve() functions if the envp parameter contains an empty string.

 

 

 

 

 

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