当 char 数组过满时，为什么我的程序 go 进入无限循环？

Question

I'm attempting to write a program in C++ that lets user enter a positive integer and a name into array with fixed size and print them out. The program seems to work correctly when I enter correct data from the first time of launching the program.

The problem I'm experiencing is when entering incorrect value for Char array (Exceeding the character count). If I enter incorrect value for char array, it gives a warning message as expected, but once I enter the correct size word, the program goes into endless loop of asking for already entered values. My code is as follows:

#include <iostream>
#include <cstring>

using namespace std;

int main()
{
    int count = 1;
    int num = 0; // variable for positive integer
    char name[31]; //char array to store name inside

    while(count != 0){

        cout << "Please enter the number: " << endl;
        cin >> num;
        while(num < 1){
            cout << "Number must be a positive integer!" << endl;  //Loop that checks whether the 
            cin >> num;                                           // entered number is a positive 
        }                                                        //  integer.

        cout << "Please enter the name: " << endl;
        cin >> name;
        while(strlen(name) > 30){                                        //Loop that checks whether the
           cout << "Name exceeds the allowed character count!" << endl; //entered name exceeds the
           cin >> name;                                                // allowed character count.
        }

        --count;
    };

    cout << num << " " << name;

    return 0;
}

I'm trying to understand why does my program go into endless loop if I enter an incorrect value first and the correct value afterwards? Is it something to do with exceeding the character count for array?

Any help would be appreciated, many thanks!

Answer 1

This loop is problematic:

 while(strlen(name) > 30) {                                        //Loop that checks whether the
       cout << "Name exceeds the allowed character count!" << endl; //entered name exceeds the
       cin >> name;                                                // allowed character count.
 }

The strlen() will return 31 if there are 31 characters followed by a '\0' . So that's already more than your 31-element long array can hold. But that's not the smallest issue - you are running into an undefined behavior territory as soon as you load more chars from cin than your array's size - as of C++17, cin will happily write past the capacity of a c-style array if you tell it to do so.

I suggest you use std::string s instead of raw C arrays. They take care of the null-terminated string technicalities for you.