BASE64可以用來將binary的字節序列數據編碼成ASCII字符序列構成的文本。完整的BASE64定義可見 RFC1421和 RFC2045。編碼后的數據比原始數據略長，為原來的4/3。在電子郵件中，根據RFC822規定，每76個字符，還需要加上一個回車換行。
轉換的時候，將三個byte的數據，先后放入一個24bit的緩沖區中，先來的byte占高位。數據不足3byte的話，于緩沖區中剩下的Bit用0補足。然后，每次取出6個bit，按照其值選擇ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/中的字符作為編碼后的輸出。不斷進行，直到全部輸入數據轉換完成。如果最后剩下兩個輸入數據，在編碼結果后加1個“=”；如果最后剩下一個輸入數據，編碼結果后加2個“=”；如果沒有剩下任何數據，就什么都不要加，這樣才可以保證資料還原的正確性。
BASE64_API.h 文件內容
/* ----------------------------------------------------------文件名稱：BASE64_API.h作者：秦建輝MSN：splashcn@msn.com當前版本：V1.1歷史版本： V1.1 2010年05月11日 修正BASE64解碼的Bug。 V1.0 2010年05月07日 完成正式版本。功能描述： BASE64編碼和解碼接口函數： Base64_Encode Base64_Decode說明： 1. 參考openssl-1.0.0。 2. 改進接口，以使其適應TCHAR字符串。 3. 修正EVP_DecodeBlock函數解碼時未去掉填充字節的缺陷。 ------------------------------------------------------------ */#pragma once#include "stdafx.h"#include <windows.h>#ifdef __cplusplusextern "C" {#endif/*功能：將二進制數據轉換成BASE64編碼字符串參數說明： inputBuffer：要編碼的二進制數據 inputCount：數據長度 outputBuffer：存儲轉換后的BASE64編碼字符串返回值： -1：參數錯誤 >=0：有效編碼長度（字符數）,不包括字符串結束符。備注： 等效于openssl中EVP_EncodeBlock函數*/INT BASE64_Encode( const BYTE* inputBuffer, INT inputCount, TCHAR* outputBuffer );/*功能：將BASE64編碼字符串轉換為二進制數據參數說明： inputBuffer：BASE64編碼字符串 inputCount：編碼長度（字符數）,應該為4的倍數。 outputBuffer：存儲轉換后的二進制數據返回值： -1：參數錯誤 -2：數據錯誤 >=0：轉換后的字節數備注： 等效于openssl中EVP_DecodeBlock函數*/INT BASE64_Decode( const TCHAR* inputBuffer, INT inputCount, BYTE* outputBuffer );#ifdef __cplusplus}#endifBASE64_API.cpp 文件內容
#pragma once#include "stdafx.h"#include "BASE64_API.h"static const CHAR* DATA_BIN2ASCII = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";INT BASE64_Encode( const BYTE* inputBuffer, INT inputCount, TCHAR* outputBuffer ){ INT i; BYTE b0, b1, b2; if( (inputBuffer == NULL) || (inputCount < 0) ) { return -1; // 參數錯誤 } if( outputBuffer != NULL ) { for( i = inputCount; i > 0; i -= 3 ) { if( i >= 3 ) { // 將3字節數據轉換成4個ASCII字符 b0 = *inputBuffer++; b1 = *inputBuffer++; b2 = *inputBuffer++; *outputBuffer++ = DATA_BIN2ASCII[b0 >> 2]; *outputBuffer++ = DATA_BIN2ASCII[((b0 << 4) | (b1 >> 4)) & 0x3F]; *outputBuffer++ = DATA_BIN2ASCII[((b1 << 2) | (b2 >> 6)) & 0x3F]; *outputBuffer++ = DATA_BIN2ASCII[b2 & 0x3F]; } else { b0 = *inputBuffer++; if( i == 2 )b1 = *inputBuffer++; else b1 = 0; *outputBuffer++ = DATA_BIN2ASCII[b0 >> 2]; *outputBuffer++ = DATA_BIN2ASCII[((b0 << 4) | (b1 >> 4)) & 0x3F]; *outputBuffer++ = (i == 1) ? TEXT('=') : DATA_BIN2ASCII[(b1 << 2) & 0x3F]; *outputBuffer++ = TEXT('='); } } // End for i *outputBuffer++ = TEXT('/0'); // 添加字符串結束標記 } return ((inputCount + 2) / 3) * 4; // 返回有效字符個數}#define B64_EOLN 0xF0 // 換行/n#define B64_CR 0xF1 // 回車/r#define B64_EOF 0xF2 // 連字符-#define B64_WS 0xE0 // 跳格或者空格（/t、space）#define B64_ERROR 0xFF // 錯誤字符#define B64_NOT_BASE64(a) (((a)|0x13) == 0xF3)static const BYTE DATA_ASCII2BIN[128] = { 0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xE0,0xF0,0xFF,0xFF,0xF1,0xFF,0xFF, 0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF, 0xE0,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0x3E,0xFF,0xF2,0xFF,0x3F, 0x34,0x35,0x36,0x37,0x38,0x39,0x3A,0x3B,0x3C,0x3D,0xFF,0xFF,0xFF,0x00,0xFF,0xFF, 0xFF,0x00,0x01,0x02,0x03,0x04,0x05,0x06,0x07,0x08,0x09,0x0A,0x0B,0x0C,0x0D,0x0E, 0x0F,0x10,0x11,0x12,0x13,0x14,0x15,0x16,0x17,0x18,0x19,0xFF,0xFF,0xFF,0xFF,0xFF, 0xFF,0x1A,0x1B,0x1C,0x1D,0x1E,0x1F,0x20,0x21,0x22,0x23,0x24,0x25,0x26,0x27,0x28, 0x29,0x2A,0x2B,0x2C,0x2D,0x2E,0x2F,0x30,0x31,0x32,0x33,0xFF,0xFF,0xFF,0xFF,0xFF};INT BASE64_Decode( const TCHAR* inputBuffer, INT inputCount, BYTE* outputBuffer ){ INT i, j; BYTE b[4]; TCHAR ch; if( (inputBuffer == NULL) || (inputCount < 0) ) { return -1; // 參數錯誤 } // 去除頭部空白字符 while( inputCount > 0 ) { ch = *inputBuffer; if( (ch < 0) || (ch >= 0x80) ) { return -2; // 數據錯誤，不在ASCII字符編碼范圍內 } else { if( DATA_ASCII2BIN[ch] == B64_WS ) { inputBuffer++; inputCount--; } else { break; } } } // 去除尾部的空白字符、回車換行字符、連字符 while( inputCount >= 4 ) { ch = inputBuffer[inputCount - 1]; if( (ch < 0) || (ch >= 0x80) ) { return -2; // 數據錯誤，不在ASCII字符編碼范圍內 } else { if( B64_NOT_BASE64(DATA_ASCII2BIN[ch]) ) { inputCount--; } else { break; } } } // 字符串長度必須為4的倍數 if( (inputCount % 4) != 0 ) { return -2; // 數據錯誤 } if( outputBuffer != NULL ) { for( i = 0; i < inputCount; i += 4 ) { for( j = 0; j < 4; j++ ) { ch = *inputBuffer++; if( (ch < 0) || (ch >= 0x80) ) { return -2; // 數據錯誤，不在ASCII字符編碼范圍內 } else { if( ch == '=' ) // 發現BASE64編碼中的填充字符 { break; } else { b[j] = DATA_ASCII2BIN[ch]; if( b[j] & 0x80 ) { return -2; // 數據錯誤，無效的Base64編碼字符 } } } } // End for j if( j == 4 ) { *outputBuffer++ = (b[0] << 2) | (b[1] >> 4); *outputBuffer++ = (b[1] << 4) | (b[2] >> 2 ); *outputBuffer++ = (b[2] << 6) | b[3]; } else if( j == 3 ) { // 有1個填充字節 *outputBuffer++ = (b[0] << 2) | (b[1] >> 4); *outputBuffer++ = (b[1] << 4) | (b[2] >> 2 ); return (i >> 2) * 3 + 2; } else if( j == 2 ) { // 有2個填充字節 *outputBuffer++ = (b[0] << 2) | (b[1] >> 4); return (i >> 2) * 3 + 1; } else { return -2; // 數據錯誤，無效的Base64編碼字符 } } // End for i } return (inputCount >> 2) * 3;}采用以上方法就可以將二進制數據轉換成可見字符進行傳遞就可以了.
那么如何使用呢?舉以下兩個例子
第一個:將一個圖片轉換成 txt 文本 并保存起來
//選擇一個圖像文件,將它轉為 文本保存至 _T("D://2.txt"void CTextPicDlg::OnBnClickedButton2(){ // TODO: 在此添加控件通知處理程序代碼 CFileDialog file(TRUE,".jpg",""); if (file.DoModal() == IDOK) { CFile data(file.GetPathName(), CFile::modeReadWrite); int len = data.GetLength(); BYTE *dv; dv = (BYTE *)malloc(len*sizeof(BYTE)); data.Read(dv, len); data.Close(); int slen = (len / 3) * 4; slen += 10; TCHAR * tc; tc = (TCHAR *)malloc(slen); slen = BASE64_Encode(dv, len, tc); CFile save(_T("D://2.txt"), CFile::modeCreate | CFile::modeWrite); save.Write(tc, slen); save.Close(); free(tc); free(dv); }}第二個例子,將一個文本文件還原為一個圖像
void CTextPicDlg::OnBnClickedButton3(){ // TODO: 在此添加控件通知處理程序代碼 CFileDialog file(TRUE, ".txt", ""); if (file.DoModal() == IDOK) { CFile data(file.GetPathName(), CFile::modeReadWrite); int len = data.GetLength(); TCHAR *dv; dv = (TCHAR *)malloc(len*sizeof(TCHAR)); data.Read(dv, len); data.Close(); int slen = (len / 4) * 3; slen += 10; BYTE * tc; tc = (BYTE *)malloc(slen); BASE64_Decode(dv, len, tc); //直接在內存里面構建CIMAGE,需要使用IStream接口,如何使用 //構建內存環境 HGLOBAL hGlobal = GlobalAlloc(GMEM_MOVEABLE, slen); void * pData = GlobalLock(hGlobal); memcpy(pData, tc, slen); // 拷貝位圖數據進去 GlobalUnlock(hGlobal); // 創建IStream IStream * pStream = NULL; if (CreateStreamOnHGlobal(hGlobal, TRUE, &pStream) != S_OK) return ; // 使用CImage加載位圖內存 CImage img; if (SUCCEEDED(img.Load(pStream)) ) { CClientDC dc(this); //使用內在中構造的圖像 直接在對話框上繪圖 img.Draw(dc.m_hDC, 0, 0, 500, 300); } //釋放內存 pStream->Release(); GlobalFree(hGlobal); //如果要保存圖像文件的話,那就使用下面的代碼 //CFileDialog savefile(FALSE, ".jpg", ""); //if (savefile.DoModal()==IDOK) //{ // CFile save(savefile.GetPathName(), CFile::modeCreate | CFile::modeWrite); // save.Write(tc, slen); // save.Close(); //} free(tc); free(dv); }}至此,利用Base64轉碼的方式,來顯示保存顯示圖片的方法,就算是成功了!
我們再來看一個base64編碼解碼的例子
首先是編碼
const BYTE Base64ValTab[65] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";#define AVal(x) Base64ValTab[x]int CSeeBase64Dlg::EncodeBase64(char * pInput, char * pOutput){ int i = 0; int loop = 0; int remain = 0; int iDstLen = 0; int iSrcLen = (int)strlen(pInput); loop = iSrcLen/3; remain = iSrcLen%3; // also can encode native char one by one as decode method // but because all of char in native string is to be encoded so encode 3-chars one time is easier. for (i=0; i < loop; i++) { BYTE a1 = (pInput[i*3] >> 2); BYTE a2 = ( ((pInput[i*3] & 0x03) << 4) | (pInput[i*3+1] >> 4) ); BYTE a3 = ( ((pInput[i*3+1] & 0x0F) << 2) | ((pInput[i*3+2] & 0xC0) >> 6) ); BYTE a4 = (pInput[i*3+2] & 0x3F); pOutput[i*4] = AVal(a1); pOutput[i*4+1] = AVal(a2); pOutput[i*4+2] = AVal(a3); pOutput[i*4+3] = AVal(a4); } iDstLen = i*4; if (remain == 1) { // should pad two equal sign i = iSrcLen-1; BYTE a1 = (pInput[i] >> 2); BYTE a2 = ((pInput[i] & 0x03) << 4); pOutput[iDstLen++] = AVal(a1); pOutput[iDstLen++] = AVal(a2); pOutput[iDstLen++] = '='; pOutput[iDstLen++] = '='; pOutput[iDstLen] = 0x00; } else if (remain == 2) { // should pad one equal sign i = iSrcLen-2; BYTE a1 = (pInput[i] >> 2); BYTE a2 = ( ((pInput[i] & 0x03) << 4) | (pInput[i+1] >> 4)); BYTE a3 = ( (pInput[i+1] & 0x0F) << 2); pOutput[iDstLen++] = AVal(a1); pOutput[iDstLen++] = AVal(a2); pOutput[iDstLen++] = AVal(a3); pOutput[iDstLen++] = '='; pOutput[iDstLen] = 0x00; } else { // just division by 3 pOutput[iDstLen] = 0x00; } return iDstLen;}下面是解碼
const BYTE Base64IdxTab[128] ={255,255,255,255, 255,255,255,255, 255,255,255,255, 255,255,255,255,255,255,255,255, 255,255,255,255, 255,255,255,255, 255,255,255,255,255,255,255,255, 255,255,255,255, 255,255,255,62, 255,255,255,63,52,53,54,55, 56,57,58,59, 60,61,255,255, 255,255,255,255,255,0,1,2, 3,4,5,6, 7,8,9,10, 11,12,13,14,15,16,17,18, 19,20,21,22, 23,24,25,255, 255,255,255,255,255,26,27,28, 29,30,31,32, 33,34,35,36, 37,38,39,40,41,42,43,44, 45,46,47,48, 49,50,51,255, 255,255,255,255};#define BVal(x) Base64IdxTab[x]int CSeeBase64Dlg::DecodeBase64(char * pInput, char * pOutput){ int i = 0; int iCnt = 0; int iSrcLen = (int)strlen(pInput); char * p = pOutput; for (i=0; i < iSrcLen; i++) { if (pInput[i] > 127) continue; if (pInput[i] == '=') return p-pOutput+1; BYTE a = BVal(pInput[i]); if (a == 255) continue; switch (iCnt) { case 0: { *p = a << 2; iCnt++; } break; case 1: { *p++ |= a >> 4; *p = a << 4; iCnt++; } break; case 2: { *p++ |= a >> 2; *p = a << 6; iCnt++; } break; case 3: { *p++ |= a; iCnt = 0; } break; } } *p = 0x00; return p-pOutput;}新聞熱點
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