[C++知识库]C++ 对txt文件的读写

#include <iostream>
#include <string>
#include <fstream>
#include <vector>
#include <algorithm>
using namespace std;

void Trim(string &str){ // 去掉字符串首尾的特殊字符 \f:换页 \v:垂直制表 \r:回车 \t:水平制表 \n:换行
    string blanks("\f\v\r\t\n");
    str.erase(0, str.find_first_not_of(blanks)); 
    str.erase(str.find_last_not_of(blanks)+1);
    
    //去掉空格
    str.erase(0, str.find_first_not_of(" "));
    str.erase(str.find_last_not_of(" ")+1);
}

int main(int argc, const char * argv[]) {
    // insert code here...
    
    /*
    filebuf fb;
    string filename = "/Users/lizhong/Documents/test/in.txt";
    if(fb.open(filename.c_str(), ios::in) == NULL){
        perror("open faild_1");
        exit(EXIT_FAILURE);
    }
    istream is(&fb);
    
   
    
    ofstream os;
    os.open("/Users/lizhong/Documents/test/out.txt", ofstream::out | ofstream::app);
    if(os.fail()){
        perror("open faild_2");
        exit(EXIT_FAILURE); //EXIT_FAILURE = 0
    }
    
  
    string input;
    while(getline(is, input,'\n')){
        auto pos = string::npos;
        pos = input.find(".");
        if(pos!=string::npos){
            os << input.substr(pos+1) << endl;
        }
    }
    fb.close();
    os.close();
    */
    
    ifstream is;
    is.open("/Users/lizhong/Documents/test/out.txt");
    if(is.fail()){
        perror("open fail_1");
        exit(EXIT_FAILURE);
    }
    
    string line;
    vector<string> str;
    while(getline(is, line, '\n')){
        Trim(line);
        if(isalpha(line[0])){
            line[0] = toupper(line[0]);
        }
        str.push_back(line);
    }
    
    sort(str.begin(), str.end(), [](string a, string b){ return a>b; });
    
    ofstream os;
    os.open("/Users/lizhong/Documents/test/out1.txt", ofstream::out | ofstream::app);
    if(os.fail()){
        perror("open_fail_2");
        exit(EXIT_FAILURE);
    }
    
    string s1;
    while(str.empty()!=true){
        s1 = str.back();
        str.pop_back();
        os << s1 << endl;
    }
    is.close();
    os.close();
    
    std::cout << "Hello, World!\n";
    return 0;
}