C++读写图片数据转成Base64格式

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

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

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

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

最近在一个项目中要实现前端传递给我们客户端的是base64的图片数据流，我们需要做的就是将它转为图片并且保存起来，根据需要再将图片存储路径信息做进一步操作。

前端传过来的字符串是这样的：

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那么这是什么呢？这是Data URI scheme。

Data URI scheme是在RFC2397中定义的，目的是将一些小的数据，直接嵌入到网页中，从而不用再从外部文件载入。比如上面那串字符，其实是一张小图片，将这些字符复制黏贴到火狐的地址栏中并转到，就能看到它了，一张1X36的白灰png图片。

在上面的Data URI中，data表示取得数据的协定名称，image/png 是数据类型名称，base64 是数据的编码方法，逗号后面就是这个image/png文件base64编码后的数据。

 

目前，Data URI scheme支持的类型有：

data:,文本数据

data:text/plain,文本数据

data:text/html,HTML代码

data:text/html;base64,base64编码的HTML代码

data:text/css,CSS代码

data:text/css;base64,base64编码的CSS代码

data:text/javascript,Javascript代码

data:text/javascript;base64,base64编码的Javascript代码

data:image/gif;base64,base64编码的gif图片数据

data:image/png;base64,base64编码的png图片数据

data:image/jpeg;base64,base64编码的jpeg图片数据

data:image/x-icon;base64,base64编码的icon图片数据

 

base64简单地说，它把一些 8-bit 数据翻译成标准 ASCII 字符，网上有很多免费的base64 编码和解码的工具，在PHP中可以用函数base64_encode() 进行编码，如echo base64_encode(file_get_contents(‘wg.png’));

目前，IE8、Firfox、Chrome、Opera浏览器都支持这种小文件嵌入。

 举个图片的例子：

网页中一张图片可以这样显示：

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

也可以这样显示：

<img src="data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAkAAAAJAQMAAADaX5RTAAAAA3NCSVQICAjb4U/gAAAABlBMVEX///+ZmZmOUEqyAAAAAnRSTlMA/1uRIrUAAAAJcEhZcwAACusAAArrAYKLDVoAAAAWdEVYdENyZWF0aW9uIFRpbWUAMDkvMjAvMTIGkKG+AAAAHHR
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把图像文件的内容直接写在了HTML 文件中，这样做的好处是，节省了一个HTTP 请求。坏处是浏览器不会缓存这种图像。

Base64.h

#ifndef _BASE64_H_
#define _BASE64_H_

#include <string>
using namespace std;

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

    /*编码
    DataByte
    [in]输入的数据长度,以字节为单位
    */
    std::string Encode(const char* Data, int DataByte);

    /*解码
    DataByte
    [in]输入的数据长度,以字节为单位
    OutByte
    [out]输出的数据长度,以字节为单位,请不要通过返回值计算
    输出数据的长度
    */
    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)
{
    //编码表
    const char EncodeTable[] = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
    //返回值
    string strEncode;
    unsigned char Tmp[] = {  };
    int LineLength = ;
    for (int i = ; i<(int)(DataByte / ); i++)
    {
        Tmp[] = *Data++;
        Tmp[] = *Data++;
        Tmp[] = *Data++;
        strEncode += EncodeTable[Tmp[] >> ];
        strEncode += EncodeTable[((Tmp[] << ) | (Tmp[] >> )) & 0x3F];
        strEncode += EncodeTable[((Tmp[] << ) | (Tmp[] >> )) & 0x3F];
        strEncode += EncodeTable[Tmp[] & 0x3F];
        if (LineLength += , LineLength == ) { strEncode += "\r\n"; LineLength = ; }
    }
    //对剩余数据进行编码
    int Mod = DataByte % ;
    if (Mod == )
    {
        Tmp[] = *Data++;
        strEncode += EncodeTable[(Tmp[] & 0xFC) >> ];
        strEncode += EncodeTable[((Tmp[] & 0x03) << )];
        strEncode += "==";
    }
    else if (Mod == )
    {
        Tmp[] = *Data++;
        Tmp[] = *Data++;
        strEncode += EncodeTable[(Tmp[] & 0xFC) >> ];
        strEncode += EncodeTable[((Tmp[] & 0x03) << ) | ((Tmp[] & 0xF0) >> )];
        strEncode += EncodeTable[((Tmp[] & 0x0F) << )];
        strEncode += "=";
    }

    return strEncode;
}

std::string CBase64::Decode(const char* Data, int DataByte, int& OutByte)
{
    //解码表
    const char DecodeTable[] =
    {
        , , , , , , , , , , , , , , , , , , , , , , , ,
        , , , , , , , , , , , , , , , , , , ,
        , // '+'
        , , ,
        , // '/'
        , , , , , , , , , , // '0'-'9'
        , , , , , , ,
        , , , , , , , , , , , , ,
        , , , , , , , , , , , , , // 'A'-'Z'
        , , , , , ,
        , , , , , , , , , , , , ,
        , , , , , , , , , , , , , // 'a'-'z'
    };
    //返回值
    string strDecode;
    int nValue;
    int i = ;
    while (i < DataByte)
    {
        if (*Data != '\r' && *Data != '\n')
        {
            nValue = DecodeTable[*Data++] << ;
            nValue += DecodeTable[*Data++] << ;
            strDecode += (nValue & 0x00FF0000) >> ;
            OutByte++;
            if (*Data != '=')
            {
                nValue += DecodeTable[*Data++] << ;
                strDecode += (nValue & 0x0000FF00) >> ;
                OutByte++;
                if (*Data != '=')
                {
                    nValue += DecodeTable[*Data++];
                    strDecode += nValue & 0x000000FF;
                    OutByte++;
                }
            }
            i += ;
        }
        else// 回车换行,跳过
        {
            Data++;
            i++;
        }
    }
    return strDecode;
}

main.cpp

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

//以下是读写图片的调用代码：
bool ReadPhotoFile(std::basic_string<TCHAR> strFileName, std::string &strData)
{
    HANDLE hFile;
    hFile = CreateFile(strFileName.c_str(), GENERIC_READ, , NULL, OPEN_EXISTING, FILE_ATTRIBUTE_NORMAL, NULL);

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

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

    if (pBuffer == NULL)
        return false;

    memset(pBuffer, , dFileSize);

    DWORD dReadSize();
    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, , NULL, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL);

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

    CBase64 base64;
    int datalen();
    DWORD dwritelen();
    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 = ; i < ;i++)
    {
        for (int j = ; j < ;j++)
        {
            if (j == )
            {

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

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

    return ;
}