#include <iostream> #include <vector> #include <string> #include <fstream> using namespace std; //从文件中读取每一行，然后消除前后空格，使其连成一个新的字符串。 int main() {     string newstring = "";     vector<string> str;     ifstream fin("a.txt");     string line;     while (getline(fin, line))         str.push_back(line);     for (unsigned i = 0; i < str.size(); i++)     {         newstring += str[i].substr(str[i].find_first_not_of(" "),str[i].find_last_not_of(" ")-str[i].find_first_not_of(" ")+1);     }     cout<<newstring<<endl;     return 0; }