C++ 操作字符串，可以打印索引字符但不能打印完整字符串

Question

I am trying to mask a password for a project I'm doing on OS X. Every masked character is appended to the string named password. But when I try to print or use the string I get nothing. However if I try to print an element of the string, I am able to. Example. cout<< password; wont print anything but cout << password[0] will print the first character of the string.

What am I doing wrong?

#include <termios.h>
#include <unistd.h>
#include <iostream>
#include <stdio.h>

using namespace std;
int getch();
int main(){
    char c;
    string password;
    int i=0;
    while( (c=getch())!= '\n'){
        password[i]=c;    
        cout << "*";
        i++;
    }

    cout<< password;
    return 0;
}
int getch() {
    struct termios oldt, newt;
    int ch;
    tcgetattr(STDIN_FILENO, &oldt);
    newt = oldt;
    newt.c_lflag &= ~(ICANON | ECHO);
    tcsetattr(STDIN_FILENO, TCSANOW, &newt);
    ch = getchar();
    tcsetattr(STDIN_FILENO, TCSANOW, &oldt);
    return ch;
}

Answer 1

When you define the object password it is starting out as empty which means any indexing into it will be out of bounds and lead to undefined behavior .

You don't need the index variable i , and you should append characters to the string:

password += c;