使用 C++ 将二进制文件 (jpg) 读取为字符串
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Read a binary file (jpg) to a string using c++
提问by zoujyjs
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++.
我需要将 jpg 文件读取为字符串。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张图片的数据。我按照前一个问题中的建议使用 c++ 将图片上传到服务器。
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?
为什么它停在60？这是60的奇怪字符，我应该怎么做才能将jpg读取为字符串？
UPDATE
更新
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!
差不多了，但是在使用建议的方法后，当我将字符串重写到输出文件时，它会失真。发现我还应该指定 ofstream 为二进制模式ofstream::binary。完毕！
By the way what's the difference between ifstream::binary& ios::binary, is there any abbreviation for ofstream::binary?
顺便说一下ifstream::binary& 和ios::binary有什么区别，有没有缩写ofstream::binary？
回答by Benjamin Lindley
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.
以二进制模式打开文件，否则它会产生有趣的行为，并且它会以不适当的方式处理某些非文本字符，至少在 Windows 上是这样。
ifstream fin("cloud.jpg", ios::binary);
Also, instead of a while loop, you can just read the whole file in one shot:
此外，您可以一次性读取整个文件，而不是 while 循环：
ostrm << fin.rdbuf();
回答by Borgleader
You shouldn't read the file to a string because it is legal for a jpg to contain values that are 0. However in a string, the value 0 has a special meaning (it's the end of string indicator aka \0). You should instead read the file into a vector. You can do this easily like so:
您不应该将文件读取为字符串，因为 jpg 包含 0 值是合法的。但是在字符串中，值 0 具有特殊含义（它是字符串指示符的结尾，也就是 \0）。您应该将文件读入向量。您可以像这样轻松地做到这一点：
#include <algorithm>
#include <iostream>
#include <fstream>
#include <vector>
int main(int argc, char* argv[])
{
std::ifstream ifs("C:\Users\Borgleader\Documents\Rapptz.h");
if(!ifs)
{
return -1;
}
std::vector<char> data = std::vector<char>(std::istreambuf_iterator<char>(ifs), std::istreambuf_iterator<char>());
//If you really need it in a string you can initialize it the same way as the vector
std::string data2 = std::string(std::istreambuf_iterator<char>(ifs), std::istreambuf_iterator<char>());
std::for_each(data.begin(), data.end(), [](char c) { std::cout << c; });
std::cin.get();
return 0;
}
回答by Jerry Coffin
Try opening the file in binary mode:
尝试以二进制模式打开文件：
ifstream fin("cloud.jpg", std::ios::binary);
At a guess, you were probably trying to read the file on Windows and the 61stcharacter was probably 0x26 -- a control-Z, which (on Windows) will be treated as marking the end of the file.
在猜测，你很可能试图读取Windows中的文件和61日字符可能是0×26 -控制-Z，它（在Windows上）会被当作标记文件的末尾。
As far as how to best do the reading, you end up with a choice between simplicity and speed, as demonstrated in a previous answer.
至于如何最好地进行阅读，您最终会在简单性和速度之间做出选择，如之前的答案所示。
