凯撒加密算法

beyes

使用 C 库实现的代码：

凯撒加密算法

使用 Windows API 读写文件版本：

[C++] 纯文本查看 复制代码

#include "stdafx.h"

#define BUF_SIZE 256

BOOL cci_f (LPCTSTR, LPCTSTR, DWORD);

VOID ReportError (LPCTSTR userMessage, DWORD exitCode, BOOL printErrorMessage)
{
    DWORD eMsglen;
    DWORD errNum = GetLastError();
  
    LPTSTR lpvSysMsg;
  
    _ftprintf(stderr, _T("%s\n"), userMessage);
  
    if (printErrorMessage) {
        eMsglen = FormatMessage(FORMAT_MESSAGE_ALLOCATE_BUFFER | FORMAT_MESSAGE_FROM_SYSTEM, NULL, errNum, MAKELANGID(LANG_NEUTRAL, SUBLANG_DEFAULT), (LPTSTR)&lpvSysMsg, 0, NULL);
  
        if (eMsglen > 0) {
            _ftprintf(stderr, _T("%s\n"), lpvSysMsg);
        }else {
            _ftprintf (stderr, _T("Last Error Number: %d.\n"), errNum);
        }
        if (lpvSysMsg != NULL)
            LocalFree(lpvSysMsg);
    }
        if (exitCode > 0)
            ExitProcess(exitCode);
  
        return;
}

int _tmain(int argc, _TCHAR* argv[])
{
    if (argc != 4)
        ReportError (_T("Usage: cci shift file1 file2"), 1, FALSE);

    if (!cci_f(argv[2], argv[3], _wtoi(argv[1])))
        ReportError(_T("Encryption failed."), 4, TRUE);

    return 0;
}

BOOL cci_f (LPCTSTR fIn, LPCTSTR fOut, DWORD shift)
{
    HANDLE hIn, hOut;

    DWORD nIn, nOut, iCopy;

    CHAR aBuffer[BUF_SIZE], ccBuffer[BUF_SIZE];

    BOOL writeOK = TRUE;

    hIn = CreateFile (fIn, GENERIC_READ, 0, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);
    if (hIn == INVALID_HANDLE_VALUE) 
        return FALSE;

    hOut = CreateFile (fOut, GENERIC_WRITE, 0, NULL, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);
    if (hOut == INVALID_HANDLE_VALUE)
        return FALSE;

    while (ReadFile(hIn, aBuffer, BUF_SIZE, &nIn, NULL) && nIn > 0 && writeOK) {
        for (iCopy = 0; iCopy < nIn; iCopy++)
            ccBuffer[iCopy] = (aBuffer[iCopy] + shift) % 256;

        writeOK = WriteFile(hOut, ccBuffer, nIn, &nOut, NULL);
    }

    CloseHandle(hIn);
    CloseHandle(hOut);

    return writeOK;
}

程序使用通用函数及变量，实现转换所有字节。