C ++中std :: ofstream的初始化向量

Question

How do I initialise a vector of std::ofstream? I am working on socket programming whereby I receive data for different symbols. For each symbol, I need to assign a separate file handle to write data to it. So, I need an array of std::ofstream. Now I want to initialise 100 of these std::ofstream. But it does not work for me. Please review the code below and suggest alternatives.

int main(){
std::vector <std::ofstream > myFilePointerMap;
std::ofstream  ofs;
    ofs.open("E:\\data\\test.txt", std::ios::app);
    for(int i=0;i<100;i++){
        myFilePointerMap.push_back( ofs);
    }
}

I am compiling using cygwin gcc in Windows eclipse.

I get the following error while compiling:

'std::ios_base& std::ios_base::operator=(const std::ios_base&)' is private line 789, external location: D:\\cygwin64\\lib\\gcc\\x86_64-pc-cygwin\\4.8.3\\include\\c++\\bits\\ios_base.h C/C++ Problem

Please help me with this.

EDIT: Let me explain what I need to done so that alternate solutions may also be supported. I need to create a object which listens to a socket. Now this socket receives upto 100 different messages which need to be written to separate files, depending upon the id (1-100) received in individual messages.

At present, I have created a vector of strings containing filepaths. The declaration in header is as follows:

std::vector <std::string> filePathMap;

Then I initialise these filepaths in the constructor as follows:

for(int i=0;i<100;i++){
    filePathMap.push_back(" ");
}

Then for random indexes between 1 to 100, when I subscribe to a message, I set the relavant filepath as

filePathMap[j]=filePath;

There after whenever I receive a message, I open the file corresponding to filePathMap and index, write to it and close it.

Originally, I wanted to create a vector of file pointers corresponding to these different symbols, so that when I receive a message, I can simply write to the file pointer, without the overhead of opening and closing each time. Therefore, I defined in my header file vector of ofstreams as follows:

    std::vector <std::ofstream > myFilePointerMap;

But in the constructor, when I put the following code, I get the error:

std::ofstream  ofs;
ofs.open("E:\\data\\test.txt", std::ios::app);
for(int i=0;i<100;i++){
    myFilePointerMap.push_back( ofs); //THIS DOES NOT COMPILE
}    

Note that I am only trying to initialise vector of myFilePointerMap to 100 so that when I assign myFilePointerMap later in the code, it should work fine.

 myFilePointerMap[j].open(filePath.c_str(),std::ios::app);

Here, j can be anything from 0-99.

Answer 1

std::ofstream is not copyable, but are movable as of C++11. Either std::move() the ofs into the vector or use a vector<> of (smart) pointers if your compiler does not support move.