Thread: Expanding Environment Variables

  1. #1
    Registered User
    Join Date
    Nov 2007

    Expanding Environment Variables

    I am trying to get the path of the system root directory by using %SystemRoot% in C code. What I originally had was:

    TCHAR szBuf[1024];
    wsprintf(szBuf, L"c:\\windows\\system32\\myapp.exe \r\n");
    Now, I want to grab the system root directory at runtime and use that instead of hardcoding in the location as on win2k, the path is "c:\winnt" or people may have installed their os on a different drive.

    I know in c++ or in c# you can use the Environment.ExpandEnvironmentVariables Method.
    String query = "My system drive is %SystemDrive% and my system root is %SystemRoot%";
    String  str = Environment.ExpandEnvironmentVariables(query);
    This will give an output of something like: "My system drive is C: and my system root is C:\WINNT"
    Is there something similar in c that I can use?

  2. #2

  3. #3
    Kernel hacker
    Join Date
    Jul 2007
    Farncombe, Surrey, England
    Or, if you actually want to expand environment variables in general, you can use getenv(), e.g.
        printf("System directory: %s\n", getenv("SystemRoot"));
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

  4. #4
    Registered User
    Join Date
    Nov 2007
    Thanks for the suggestions! I was able to get it working like so...

    TCHAR szBuf[1024];
    TCHAR szMyApp[1024];
    wchar_t systemrootpath[64]= L"";
    wchar_t dname[64]=L"";
    wsprintf(szBuf, L"%s", getenv("SystemRoot"));
    mbstowcs(systemrootpath, szBuf, 64);  // Convert to unicode
    wsprintf(szMyApp,L"%s\\system32\\myapp.exe %s\0", systemrootpath, dname);

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