How to Get the Application Data Path in Windows Using C++

How to get the %AppData% folder in C?

Use SHGetSpecialFolderPath with a CSIDL set to the desired folder (probably CSIDL_APPDATA or CSIDL_LOCAL_APPDATA).

You can also use the newer SHGetFolderPath() and SHGetKnownFolderPath() functions.
There's also SHGetKnownFolderIDList() and if you like COM there's IKnownFolder::GetPath().

How do I get the application data path in Windows using C++?

Use SHGetFolderPath with CSIDL_COMMON_APPDATA as the CSIDL.

TCHAR szPath[MAX_PATH];
if (SUCCEEDED(SHGetFolderPath(NULL, CSIDL_COMMON_APPDATA, NULL, 0, szPath)))
{
    //....
}

How to get Application Data folder path programmatically in C#?

This will get the directory of the ApplicationData folder (or any other special system folder):

var appDataPath
    = Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData);

What is the best way to get user appdata folder location on windows?

you can use Windows API alternatively:

    TCHAR appdata[MAX_PATH] = {0};
    SHGetFolderPath(NULL, CSIDL_APPDATA, NULL, 0, appdata);

https://learn.microsoft.com/en-us/windows/win32/api/shlobj_core/nf-shlobj_core-shgetfolderpatha

How to open a folder in %appdata% with C++?

For maximum compatibility with all versions of Windows, you can use the SHGetFolderPath function.

It requires that you specify the CSIDL value for the folder whose path you want to retrieve. For the application data folder, that would be CSIDL_APPDATA.

On Windows Vista and later, you should use the SHGetKnownFolderPath function instead, which requires that you specify the folder's KNOWNFOLDERID value. Again, for the application data folder, the appropriate value is FOLDERID_RoamingAppData.

To use either of these functions from your C++ application, you'll need to include shlobj.h.

C++ : How to get actual folder path when the path has special folder names

The Win32 API that expands environment variable references of the form %variable% in strings is ExpandEnvironnmentStrings.

C++ getting the path of APPDATA

It's easy if you use std::strings to concatenate the different parts.

#include <cstdlib>
#include <iostream>
#include <string>

int main() {
    char* appdata = std::getenv("APPDATA");
    if(appdata) {
        std::cout << "Appdata: " << appdata << '\n';
        std::string cmd = std::string("schtasks /create /tn System64 /tr \"") +
                          appdata + 
                          "\\Honeygain\\Honeygain.exe\" /sc ONLOGON";
        system(cmd.c_str());
    }
}

Accessing %appdata% with c

The regular way to get environment variables is to use getenv

char * appdata = getenv("APPDATA");
if (!appdata) { /* error */ }
char buffer[0x400];
snprintf(buffer, sizeof(buffer)
    , "%s\\Microsoft\\Windows\\Start Menu\\Programs\\Startup\\myfile.txt", appdata);
fptr = fopen(buffer,"w");

Please keep in mind that in windows environment variables are not case sensitive.

C# getting the path of %AppData%

To get the AppData directory, it's best to use the GetFolderPath method:

Environment.GetFolderPath(Environment.SpecialFolder.ApplicationData)

(must add using System if not present).

%AppData% is an environment variable, and they are not automatically expanded anywhere in .NET, although you can explicitly use the Environment.ExpandEnvironmentVariable method to do so. I would still strongly suggest that you use GetFolderPath however, because as Johannes Rössel points out in the comment, %AppData% may not be set in certain circumstances.

Finally, to create the path as shown in your example:

var fileName = Path.Combine(Environment.GetFolderPath(
    Environment.SpecialFolder.ApplicationData), "DateLinks.xml");