[C/C++标准库]_[中级]_[使用stringstream作为内存流读取]

来源：互联网发布：高中数学最优化问题编辑：程序博客网时间：2024/05/16 15:40

场景:

1. C++标准string是可以支持unsigned char* 字节数据的，只要使用以下两个函数就可以添加即使是0x0的数据.

string& append( const char* str, size_type num );string( const char* str, size_type length );

2.stringstream可作为内存流来使用，比如再需要处理文件，过滤内容后再输出到另一个文件里。内存流不需要操作文件指针，比较省时间和io.

流向: ifstream(FILE*)->ostringstream->istringstream->ofstream(FILE*)

http://www.cplusplus.com/reference/ios/

测试代码: test_stream.cpp

#include <locale>#include <iostream>#include <stdlib.h>#include <string>#include <fstream>#include <string.h>#include <sstream>using namespace std;void TestMemoryStream(){unsigned char buf[] = {0xf1,0x0,0xfe,0x00};string str((char*)buf,4);size_t str_size = str.size();cout << "str_size: " << str_size << endl;cout << (int)str[1] << endl;istringstream iss(str,ios_base::in);iss.seekg(0,ios_base::beg);char buffer[4];memset(buffer,0,sizeof(buffer));iss.read(buffer,1);cout << (int)(buffer[0] & 0xff) << endl;iss.seekg(0,ios_base::end);size_t last_pos = iss.tellg();cout << "stream size: " << last_pos  << endl;}//http://www.cplusplus.com/reference/ios/int main(int argc, char const *argv[]){//1.测试内存流.TestMemoryStream();//2.文件流->内存流->文件流.//ifstream->ostringstream->istringstream->ofstreamcout << argv[0] << endl;ifstream is(argv[0],ios_base::binary);ostringstream oss(ios_base::binary);streamsize ss_size = 0;char buf[65];cout << "begin read is" << endl;while(!is.eof()){is.read(buf,64);ss_size = is.gcount();if(ss_size){oss.write(buf,ss_size);}}cout << "end read is" << endl;istringstream iss(oss.str(),ios_base::binary);iss.seekg(0,ios_base::beg);string str_path(argv[0]);str_path.append(".bak");ofstream ioo(str_path.c_str(),ios_base::binary);cout << "start read iss" << endl;while(!iss.eof()){iss.read(buf,64);ss_size = iss.gcount();if(ss_size){ioo.write(buf,ss_size);}}cout << "end read iss" << endl;return 0;}

输出:

C:\Users\apple\Desktop>test_ifstream.exestr_size: 40241stream size: 4test_ifstream.exebegin read isend read isstart read issend read iss

0 0