WriteProcessMemory

The WriteProcessMemory function writes data to an area of memory in a specified process. The entire area to be written to must be accessible, or the operation fails.

BOOL WriteProcessMemory(
  HANDLE hProcess,               // handle to process
  LPVOID lpBaseAddress,          // base of memory area
  LPVOID lpBuffer,               // data buffer
  DWORD nSize,                   // number of bytes to write
  LPDWORD lpNumberOfBytesWritten // number of bytes written
);

Parameters

hProcess

[in] Handle to the process whose memory is to be modified. The handle must have PROCESS_VM_WRITE and PROCESS_VM_OPERATION access to the process.

lpBaseAddress

[in] Pointer to the base address in the specified process to which data will be written. Before any data transfer occurs, the system verifies that all data in the base address and memory of the specified size is accessible for write access. If this is the case, the function proceeds; otherwise, the function fails.

lpBuffer

[in] Pointer to the buffer that contains data to be written into the address space of the specified process.

nSize

[in] Specifies the requested number of bytes to write into the specified process.

lpNumberOfBytesWritten

[out] Pointer to a variable that receives the number of bytes transferred into the specified process. This parameter is optional. If lpNumberOfBytesWritten is NULL, the parameter is ignored.

Return Values

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. The function will fail if the requested write operation crosses into an area of the process that is inaccessible.

Remarks

WriteProcessMemory copies the data from the specified buffer in the current process to the address range of the specified process. Any process that has a handle with PROCESS_VM_WRITE and PROCESS_VM_OPERATION access to the process to be written to can call the function. The process whose address space is being written to is typically, but not necessarily, being debugged.

The entire area to be written to must be accessible. If it is not, the function fails as noted previously.

Requirements

  Windows NT/2000: Requires Windows NT 3.1 or later.
  Windows 95/98: Requires Windows 95 or later.
  Header: Declared in Winbase.h; include Windows.h.
  Library: Use Kernel32.lib.

See Also

Debugging Overview, Debugging Functions, ReadProcessMemory