Siehe Platform/Windows-SDK:
GetEnvironmentVariable
Retrieves the contents of the specified variable from the environment block of the calling process.
DWORD WINAPI GetEnvironmentVariable(
LPCTSTR lpName,
LPTSTR lpBuffer,
DWORD nSize
);
Parameters
lpName [in] The name of the environment variable. lpBuffer [out] A pointer to a buffer that receives the contents of the specified environment variable as a null-terminated string. An environment variable has a maximum size limit of 32,767 characters, including the null-terminating character. nSize [in] The size of the buffer pointed to by the lpBuffer parameter, in characters. Return Value
If the function succeeds, the return value is the number of characters stored in the buffer pointed to by lpBuffer, not including the terminating null character.
If lpBuffer is not large enough to hold the data, the return value is the buffer size, in characters, required to hold the string and its terminating null character.
If the function fails, the return value is zero. If the specified environment variable was not found in the environment block, GetLastError returns ERROR_ENVVAR_NOT_FOUND.
