MSDN Documentation

Windows API Reference

System Functions

This section provides documentation for Win32 API functions related to system-level operations, including process and thread management, system information retrieval, and time services.

Core System Functions

GetCurrentProcessId

Syntax

DWORD GetCurrentProcessId();

Parameters

This function has no parameters.

Return Value

The return value is the process identifier of the calling process.

Remarks

The process identifier is a 32-bit value that uniquely identifies the calling process on the system. This value is not guaranteed to be contiguous and can be reused after the process terminates.

See Also

GetCurrentThreadId

Syntax

DWORD GetCurrentThreadId();

Parameters

This function has no parameters.

Return Value

The return value is the thread identifier of the calling thread.

Remarks

The thread identifier is a 32-bit value that uniquely identifies the calling thread on the system. This value is not guaranteed to be contiguous and can be reused after the thread terminates.

See Also

GetTickCount

Syntax

DWORD GetTickCount();

Parameters

This function has no parameters.

Return Value

The return value is the number of milliseconds that have elapsed since the system was started. This function returns approximately every 49.7 days.

Remarks

Do not use the return value of GetTickCount to calculate elapsed time. The value wraps around to 0 every 49.7 days. For time intervals longer than a few minutes, use the GetSystemTimeAsFileTime function.

See Also

GetSystemTimes

Syntax

BOOL GetSystemTimes(
  LPFILETIME lpIdleTime,
  LPFILETIME lpKernelTime,
  LPFILETIME lpUserTime
);

Parameters

  • lpIdleTime: A pointer to a FILETIME structure that receives the amount of time the system has been idle.
  • lpKernelTime: A pointer to a FILETIME structure that receives the amount of time the system has spent in kernel mode.
  • lpUserTime: A pointer to a FILETIME structure that receives the amount of time the system has spent in user mode.

Return Value

If the function succeeds, the return value is nonzero. If the function fails, the return value is zero. To get extended error information, call GetLastError.

Remarks

The FILETIME structures receive values representing the total time the CPU has spent in each mode since the system was started. These values are independent of the GetTickCount rollover.

See Also

GetComputerName

Syntax

BOOL GetComputerName(
  LPTSTR lpBuffer,
  LPDWORD nSize
);

Parameters

  • lpBuffer: A pointer to a buffer that receives the null-terminated string specifying the computer name.
  • nSize: A pointer to a DWORD variable that specifies the size, in characters, of the buffer pointed to by lpBuffer. On input, this is the size of the buffer. On output, this is the number of characters copied to the buffer, not including the terminating null character.

Return Value

If the function succeeds, the return value is nonzero. If the function fails, the return value is zero. To get extended error information, call GetLastError.

Remarks

The computer name is the name assigned to the local computer. If the computer is a node in a domain, the name returned is the NetBIOS name of the computer.

See Also

GetUserName

Syntax

BOOL GetUserName(
  LPTSTR lpBuffer,
  LPDWORD pcbBuffer
);

Parameters

  • lpBuffer: A pointer to a buffer that receives the null-terminated string specifying the user name.
  • pcbBuffer: A pointer to a DWORD variable that specifies the size, in characters, of the buffer pointed to by lpBuffer. On input, this is the size of the buffer. On output, this is the number of characters copied to the buffer, not including the terminating null character.

Return Value

If the function succeeds, the return value is nonzero. If the function fails, the return value is zero. To get extended error information, call GetLastError.

Remarks

The user name is the name of the user who is currently logged on to the system. The name is typically in the form "DomainName\UserName" or "ComputerName\UserName".

See Also

GetWindowsDirectory

Syntax

UINT GetWindowsDirectory(
  LPTSTR lpBuffer,
  UINT   uSize
);

Parameters

  • lpBuffer: A pointer to a buffer that receives the null-terminated string specifying the path to the Windows directory.
  • uSize: The size, in characters, of the buffer pointed to by lpBuffer.

Return Value

If the function succeeds, the return value is the length, in characters, of the string copied to lpBuffer, not including the terminating null character. If the buffer is not large enough for the path, the return value is the size of the buffer required to hold the path, in characters, including the terminating null character. If the function fails, the return value is zero. To get extended error information, call GetLastError.

Remarks

This function retrieves the full path to the Windows directory. The path does not end with a backslash.

See Also

GetSystemDirectory

Syntax

UINT GetSystemDirectory(
  LPTSTR lpBuffer,
  UINT   uSize
);

Parameters

  • lpBuffer: A pointer to a buffer that receives the null-terminated string specifying the path to the system directory.
  • uSize: The size, in characters, of the buffer pointed to by lpBuffer.

Return Value

If the function succeeds, the return value is the length, in characters, of the string copied to lpBuffer, not including the terminating null character. If the buffer is not large enough for the path, the return value is the size of the buffer required to hold the path, in characters, including the terminating null character. If the function fails, the return value is zero. To get extended error information, call GetLastError.

Remarks

This function retrieves the full path to the system directory. The system directory contains files that are necessary for the operating system to run, such as device drivers and system DLLs. The path does not end with a backslash.

See Also