每次读取部分文件到内存中

std::fstream fin("fine.name",std::fstream::in|std::fstream::ate);
    if(fin.good()) {
        size_t file_size=fin.tellg();
        fin.seekg(0,std::fstream::beg);
        
        size_t read_per=100;
        size_t read_sum=0;
        std::vector<char> file_data_vec(read_per,0);

        while(read_sum<file_size) {
            size_t read_can=std::min(read_per,file_size-read_sum);
            fin.read(file_data_vec.data(),read_can);
            read_sum+=read_can;
            //operation
        }
        fin.close();
    }