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I need to read a whole file into memory and place it in a C++ std::string . 我需要将整个文件读入内存并将其放在C ++ std::string 。

If I were to read it into a char[] , the answer would be very simple: 如果我将其读入char[] ，答案将非常简单：

std::ifstream t;int length;t.open("file.txt");      // open input filet.seekg(0, std::ios::end);    // go to the endlength = t.tellg();           // report location (this is the length)t.seekg(0, std::ios::beg);    // go back to the beginningbuffer = new char[length];    // allocate memory for a buffer of appropriate dimensiont.read(buffer, length);       // read the whole file into the buffert.close();                    // close file handle// ... Do stuff with buffer here ...

Now, I want to do the exact same thing, but using a std::string instead of a char[] . 现在，我想做完全相同的事情，但是使用std::string而不是char[] 。 I want to avoid loops, ie I don't want to: 我想避免环路，即我不想 ：

std::ifstream t;t.open("file.txt");std::string buffer;std::string line;while(t){std::getline(t, line);// ... Append line to buffer and go on}t.close()

Any ideas? 有任何想法吗？

#1楼

参考：

#2楼

I could do it like this: 我可以这样做：

void readfile(const std::string &filepath,std::string &buffer){    std::ifstream fin(filepath.c_str());    getline(fin, buffer, char(-1));    fin.close();}

If this is something to be frowned upon, please let me know why 如果您对此不满意，请告诉我为什么

#3楼

I think best way is to use string stream. 我认为最好的方法是使用字符串流。 simple and quick !!! 简单快捷！

#include 
   
    #include 
    
     #include 
     
       //std::stringstreamint main() {    std::ifstream inFile;    inFile.open("inFileName"); //open the input file    std::stringstream strStream;    strStream << inFile.rdbuf(); //read the file    std::string str = strStream.str(); //str holds the content of the file    std::cout << str << "\n"; //you can do anything with the string!!!}
     
    
   

#4楼

I figured out another way that works with most istreams, including std::cin! 我想出了适用于大多数istream的另一种方法，包括std :: cin！

std::string readFile(){    stringstream str;    ifstream stream("Hello_World.txt");    if(stream.is_open())    {        while(stream.peek() != EOF)        {            str << (char) stream.get();        }        stream.close();        return str.str();    }}

#5楼

Update: Turns out that this method, while following STL idioms well, is actually surprisingly inefficient! 更新：事实证明，这种方法虽然很好地遵循了STL习惯用法，但实际上效率低得多！ Don't do this with large files. 不要对大文件执行此操作。 (See: ) （请参阅： : ）

You can make a streambuf iterator out of the file and initialize the string with it: 您可以从文件中制作一个streambuf迭代器，并使用它初始化字符串：

#include 
   
    #include 
    
     #include 
     
      std::ifstream t("file.txt");std::string str((std::istreambuf_iterator
      
       (t)),                 std::istreambuf_iterator
       
        ());
       
      
     
    
   

Not sure where you're getting the t.open("file.txt", "r") syntax from. 不知道从哪里获取t.open("file.txt", "r")语法。 As far as I know that's not a method that std::ifstream has. 据我所知，这不是std::ifstream具有的方法。 It looks like you've confused it with C's fopen . 您似乎已经将其与C的fopen混淆了。

Edit: Also note the extra parentheses around the first argument to the string constructor. 编辑：还请注意字符串构造函数的第一个参数周围的多余括号。 These are essential . 这些是必不可少的 。 They prevent the problem known as the " ", which in this case won't actually give you a compile error like it usually does, but will give you interesting (read: wrong) results. 它们可以防止称为“ ”的问题，在这种情况下，它实际上不会像通常那样给您带来编译错误，但会给您带来有趣的（错误的）结果。

Following KeithB's point in the comments, here's a way to do it that allocates all the memory up front (rather than relying on the string class's automatic reallocation): 遵循KeithB在评论中的观点，这是一种预先分配所有内存的方法（而不是依赖于字符串类的自动重新分配）：

#include 
   
    #include 
    
     #include 
     
      std::ifstream t("file.txt");std::string str;t.seekg(0, std::ios::end);   str.reserve(t.tellg());t.seekg(0, std::ios::beg);str.assign((std::istreambuf_iterator
      
       (t)),            std::istreambuf_iterator
       
        ());
       
      
     
    
   

#6楼

I don't think you can do this without an explicit or implicit loop, without reading into a char array (or some other container) first and ten constructing the string. 我认为如果没有显式或隐式循环，而没有先读入char数组（或其他容器），又没有十个构造字符串的方法，您将无法做到这一点。 If you don't need the other capabilities of a string, it could be done with vector<char> the same way you are currently using a char * . 如果不需要字符串的其他功能，则可以使用vector<char>来完成，就像您当前使用char * 。

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