使用c ++读取二进制文件（jpg）到字符串 [英] Read a binary file (jpg) to a string using c++

问题描述

我需要读一个jpg文件到一个字符串。我想把这个文件上传到我们的服务器，我只是发现，API需要一个字符串作为这个pic的数据。我按照先前问题中的建议上传图片到服务器使用c ++ 。

  int main（）{
 ifstream fin（cloud.jpg）; 
 ofstream fout（test.jpg）; //为测试目的，看看字符串是否是正确的副本
 ostringstream ostrm; 
 
 unsigned char tmp; 
 int count = 0; 
 while（fin>> tmp）{
 ++ count; //用于测试目的
 ostrm< tmp; 
} 
 string data（ostrm.str（））; 
 cout<< count<< endl; // ouput 60！肯定不是正确的大小
 fout< string; //只有60个字节
 return 0; 
} 
  

为什么在60时停止？这是一个奇怪的字符在60，我应该怎么做把jpg读到一个字符串？

UPDATE

几乎存在，但使用建议的方法后，将字符串重写到输出文件，它扭曲。发现我还应该通过 ofstream :: binary 指定ofstream是二进制模式。完成！

顺便说一句， ifstream :: binary ios :: binary ，是否有任何缩写 ofstream :: binary ？

以二进制模式打开文件，否则它会有一些有趣的行为，它会以不当的方式处理某些非文本字符，至少在Windows上。 p>

  ifstream fin（cloud.jpg，ios :: binary）; 
  

此外，而不是while循环，你可以一次读取整个文件：

  ostrm<< fin.rdbuf（）; 
  

I need to read a jpg file to a string. I want to upload this file to our server, I just find out that the API requires a string as the data of this pic. I followed the suggestions in a former question I've asked Upload pics to a server using c++ .

int main() {
    ifstream fin("cloud.jpg");
    ofstream fout("test.jpg");//for testing purpose, to see if the string is a right copy
    ostringstream ostrm;

    unsigned char tmp;
    int count = 0;
    while ( fin >> tmp ) {
        ++count;//for testing purpose
        ostrm << tmp;
    }
    string data( ostrm.str() );
    cout << count << endl;//ouput 60! Definitely not the right size
    fout << string;//only 60 bytes
    return 0;
}

Why it stops at 60? It's a strange character at 60, and what should I do to read the jpg to a string?

UPDATE

Almost there, but after using the suggested method, when I rewrite the string to the output file, it distorted. Find out that I should also specify that the ofstream is in binary mode by ofstream::binary. Done!

By the way what's the difference between ifstream::binary & ios::binary, is there any abbreviation for ofstream::binary?

解决方案

Open the file in binary mode, otherwise it will have funny behavior, and it will handle certain non-text characters in inappropriate ways, at least on Windows.

ifstream fin("cloud.jpg", ios::binary);

Also, instead of a while loop, you can just read the whole file in one shot:

ostrm << fin.rdbuf();

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