C++讀寫圖片數據轉成Base64格式

轉載：http://www.cnblogs.com/jeray/p/8746976.html

轉載：https://www.cnblogs.com/lujin49/p/4957742.html

轉載：https://blog.csdn.net/whish1994/article/details/79894451

轉載：https://blog.csdn.net/gu_wen_jie/article/details/79050287

最近在一個項目中要實現前端傳遞給我們客戶端的是base64的圖片數據流，我們需要做的就是將它轉為圖片並且保存起來，根據需要再將圖片存儲路徑信息做進一步操作。

前端傳過來的字符串是這樣的：

<img src="data:image/jpg;base64,iVBORw0KGgoAAAANSUhEUgAAAKAAAAAwCAMAAAChd4FcAAAAA3NCSVQICAjb4U/gAAACRlBMVEUAAADi6OSMjIxSUlIrXja5trg8rFEDRhErokJ8w4pJrVxmZmYERRIinTn++P07nk/X0Naww7Stra0pdTj37/dlunUXWiS53L+ZmZmOy5pahGJKdVIQE
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2vcLM2kLvKHfZkv4Wp35NAkFVdccNdWlt8E1lt6cSjigv8J/SeRBARYfPWXF/n29zczr658cvwE3vTJJrUQHmeP9Iy3m9mB7zthJ/M287/AdxppEv2qVN4AAAAAElFTkSuQmCC" />

那么這是什么呢？這是Data URI scheme。

Data URI scheme是在RFC2397中定義的，目的是將一些小的數據，直接嵌入到網頁中，從而不用再從外部文件載入。比如上面那串字符，其實是一張小圖片，將這些字符復制黏貼到火狐的地址欄中並轉到，就能看到它了，一張1X36的白灰png圖片。

在上面的Data URI中，data表示取得數據的協定名稱，image/png 是數據類型名稱，base64 是數據的編碼方法，逗號后面就是這個image/png文件base64編碼后的數據。

 

目前，Data URI scheme支持的類型有：

data:,文本數據

data:text/plain,文本數據

data:text/html,HTML代碼

data:text/html;base64,base64編碼的HTML代碼

data:text/css,CSS代碼

data:text/css;base64,base64編碼的CSS代碼

data:text/javascript,Javascript代碼

data:text/javascript;base64,base64編碼的Javascript代碼

data:image/gif;base64,base64編碼的gif圖片數據

data:image/png;base64,base64編碼的png圖片數據

data:image/jpeg;base64,base64編碼的jpeg圖片數據

data:image/x-icon;base64,base64編碼的icon圖片數據

 

base64簡單地說，它把一些 8-bit 數據翻譯成標准 ASCII 字符，網上有很多免費的base64 編碼和解碼的工具，在PHP中可以用函數base64_encode() 進行編碼，如 echo base64_encode(file_get_contents(‘wg.png’));

目前，IE8、Firfox、Chrome、Opera瀏覽器都支持這種小文件嵌入。

 舉個圖片的例子：

網頁中一張圖片可以這樣顯示：

<img src="http://mail.163.com/images/x.png" />

也可以這樣顯示：

<img src="data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAkAAAAJAQMAAADaX5RTAAAAA3NCSVQICAjb4U/gAAAABlBMVEX///+ZmZmOUEqyAAAAAnRSTlMA/1uRIrUAAAAJcEhZcwAACusAAArrAYKLDVoAAAAWdEVYdENyZWF0aW9uIFRpbWUAMDkvMjAvMTIGkKG+AAAAHHR
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把圖像文件的內容直接寫在了HTML 文件中，這樣做的好處是，節省了一個HTTP 請求。壞處是瀏覽器不會緩存這種圖像。

 

Base64.h

#ifndef _BASE64_H_
#define _BASE64_H_

#include <string>
using namespace std;

class CBase64
{
public:
public:
    CBase64();
    ~CBase64();

    /*編碼
    DataByte
    [in]輸入的數據長度,以字節為單位
    */
    std::string Encode(const char* Data, int DataByte);

    /*解碼
    DataByte
    [in]輸入的數據長度,以字節為單位
    OutByte
    [out]輸出的數據長度,以字節為單位,請不要通過返回值計算
    輸出數據的長度
    */
    std::string Decode(const char* Data, int DataByte, int& OutByte);

};
#endif//_BASE64_H_

Base64.cpp

#include"Base64.h"

CBase64::CBase64()
{

}

CBase64::~CBase64()
{

}

std::string CBase64::Encode(const char* Data, int DataByte)
{
    //編碼表  
    const char EncodeTable[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
    //返回值  
    string strEncode;
    unsigned char Tmp[4] = { 0 };
    int LineLength = 0;
    for (int i = 0; i<(int)(DataByte / 3); i++)
    {
        Tmp[1] = *Data++;
        Tmp[2] = *Data++;
        Tmp[3] = *Data++;
        strEncode += EncodeTable[Tmp[1] >> 2];
        strEncode += EncodeTable[((Tmp[1] << 4) | (Tmp[2] >> 4)) & 0x3F];
        strEncode += EncodeTable[((Tmp[2] << 2) | (Tmp[3] >> 6)) & 0x3F];
        strEncode += EncodeTable[Tmp[3] & 0x3F];
        if (LineLength += 4, LineLength == 76) { strEncode += "\r\n"; LineLength = 0; }
    }
    //對剩余數據進行編碼  
    int Mod = DataByte % 3;
    if (Mod == 1)
    {
        Tmp[1] = *Data++;
        strEncode += EncodeTable[(Tmp[1] & 0xFC) >> 2];
        strEncode += EncodeTable[((Tmp[1] & 0x03) << 4)];
        strEncode += "==";
    }
    else if (Mod == 2)
    {
        Tmp[1] = *Data++;
        Tmp[2] = *Data++;
        strEncode += EncodeTable[(Tmp[1] & 0xFC) >> 2];
        strEncode += EncodeTable[((Tmp[1] & 0x03) << 4) | ((Tmp[2] & 0xF0) >> 4)];
        strEncode += EncodeTable[((Tmp[2] & 0x0F) << 2)];
        strEncode += "=";
    }

    return strEncode;
}

std::string CBase64::Decode(const char* Data, int DataByte, int& OutByte)
{
    //解碼表  
    const char DecodeTable[] =
    {
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        62, // '+'  
        0, 0, 0,
        63, // '/'  
        52, 53, 54, 55, 56, 57, 58, 59, 60, 61, // '0'-'9'  
        0, 0, 0, 0, 0, 0, 0,
        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, // 'A'-'Z'  
        0, 0, 0, 0, 0, 0,
        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, // 'a'-'z'  
    };
    //返回值  
    string strDecode;
    int nValue;
    int i = 0;
    while (i < DataByte)
    {
        if (*Data != '\r' && *Data != '\n')
        {
            nValue = DecodeTable[*Data++] << 18;
            nValue += DecodeTable[*Data++] << 12;
            strDecode += (nValue & 0x00FF0000) >> 16;
            OutByte++;
            if (*Data != '=')
            {
                nValue += DecodeTable[*Data++] << 6;
                strDecode += (nValue & 0x0000FF00) >> 8;
                OutByte++;
                if (*Data != '=')
                {
                    nValue += DecodeTable[*Data++];
                    strDecode += nValue & 0x000000FF;
                    OutByte++;
                }
            }
            i += 4;
        }
        else// 回車換行,跳過  
        {
            Data++;
            i++;
        }
    }
    return strDecode;
}

main.cpp

#include "Base64.h"
#include <tchar.h>
#include <windows.h>
#include <iostream>
using namespace std;

//以下是讀寫圖片的調用代碼：
bool ReadPhotoFile(std::basic_string<TCHAR> strFileName, std::string &strData)
{
    HANDLE hFile;
    hFile = CreateFile(strFileName.c_str(), GENERIC_READ, 0, NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);

    if (hFile == INVALID_HANDLE_VALUE)
    {
        return false;
    }

    DWORD dFileSize = GetFileSize(hFile, NULL);
    char * pBuffer = new char[dFileSize + 1];

    if (pBuffer == NULL)
        return false;

    memset(pBuffer, 0, dFileSize);

    DWORD dReadSize(0);
    if (!ReadFile(hFile, pBuffer, dFileSize, &dReadSize, NULL))
    {
        delete[]pBuffer;
        CloseHandle(hFile);
        return false;
    }

    CBase64 base64;
    strData = "";
    strData = base64.Encode((const char*)pBuffer, dReadSize);

    delete[]pBuffer;
    CloseHandle(hFile);
    return true;
}

bool WritePhotoFile(std::basic_string<TCHAR> strFileName, std::string &strData)
{
    HANDLE hFile;
    hFile = CreateFile(strFileName.c_str(), GENERIC_WRITE, 0, NULL, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);

    if (hFile == INVALID_HANDLE_VALUE)
    {
        return false;
    }

    CBase64 base64;
    int datalen(0);
    DWORD dwritelen(0);
    std::string strdcode = base64.Decode(strData.data(), strData.size(), datalen);
    if (!WriteFile(hFile, strdcode.data(), datalen, &dwritelen, NULL))
    {
        CloseHandle(hFile);
        return false;
    }
    CloseHandle(hFile);
    return true;
}int main()
{
    wstring path = L"C:\\Users\\Administrator\\Desktop\\test.jpg";
    string data;
    ReadPhotoFile(path, data);

    wstring strfilename = L"C:\\Users\\Administrator\\Desktop\\123.jpg";

    WritePhotoFile(strfilename, data);



    for (int i = 0; i < 10;i++)
    {
        for (int j = 0; j < 5;j++)
        {
            if (j == 3)
            {

                break;
            }
            cout << "j=" << j << endl;
        }

        cout << "i=" << i << endl;
    }

    return 0;
}