在抛出“std::logic_error”实例后调用终止 what(): basic_string::_M_construct null 无效（帮助）

Question

The compiler doesn't run into any errors, but as soon as my program runs, it hits me with this error. terminate called after throwing an instance of 'std::logic_error' what(): basic_string::_M_construct null not valid

This is the code:

#include<iostream>
#include<iomanip>
#include<string>
#include<conio.h>
#include<stdio.h>
using namespace std;

int prodnum, brandnum;

struct desc{
    string name;
    float price;
    int stock;
    int sold;
};

struct assets{
    string prodname;
    desc arr_description[8] = {0};
};

assets arr_assets[8] = {0};

void login();

int main()
{
    login();
    system("cls");
    cout<<"            ***** INVENTORY SYSTEM C++ *****"<<endl
        <<"Enter Number of Products for Inventory: ";
    cin>>prodnum;
     
    for(int i = 0; i < prodnum; i++){
        cout<<"Product "<<i<<": ";
        cin>>arr_assets[i].prodname;
        cout<<"How many "<<arr_assets[i].prodname<<"? ";
        cin>>brandnum;
        cout<<endl;
        cout<<"Name: ";
        cin>>arr_assets[i].arr_description[i].name;
        cout<<endl;
        cout<<"Price: ";
        cin>>arr_assets[i].arr_description[i].price;
        cout<<endl;
        cout<<"Stock: ";
        cin>>arr_assets[i].arr_description[i].stock;
        cout<<"Sold: ";
        cin>>arr_assets[i].arr_description[i].sold;
    }
    system("cls");
    cout<<"            ***** INVENTORY SYSTEM C++ *****\n";
    cout<<"Product No."<<setw(7)<<"Product"<<setw(7)<<"Name"<<setw(7)<<"Price"<<setw(7)<<"Stock"<<setw(7)<<"Sold"<<setw(7)<<"Left\n";
    for(int i = 0; i < prodnum; i++){
        for(int j = 0; j < brandnum; j++){
            cout<<"  ["<<i<<"]  "<<setw(7)
                <<arr_assets[i].prodname<<setw(7)
                <<arr_assets[i].arr_description[j].name<<setw(7)
                <<arr_assets[i].arr_description[j].price<<setw(7)
                <<arr_assets[i].arr_description[j].stock<<setw(7)
                <<arr_assets[i].arr_description[j].sold<<setw(7)
                <<arr_assets[i].arr_description[j].stock - arr_assets[i].arr_description[j].sold;
        }
    }
}

void login()
{
    int attempt = 0;
    bool success = false;
    string correctU = "admin";
    string correctP = "Exer04\r";
    string username, password;
    char pword[100];
    while(attempt < 3 && !success){
        system("cls");
        cout<<"Enter Username: ";
        cin>>username;
        cout<<"Enter Password: ";
        for(int i = 0; i < 100; i++){
            pword[i] = _getch();
            _putch('*');
            if(pword[i] == 13){
                break;
            }
        }
        password = pword;
        cout<<endl;
        try{
            if(username != correctU){
                throw invalid_argument("Invalid Username");
            }
            if(password != correctP){
                throw invalid_argument("Invalid Password");
            }
            if(username != correctU && password != correctP){
                throw invalid_argument("Invalid Username and Password");
            }
            success = true;
        }
        catch(const invalid_argument& e){
            cout<<"Error: "<<e.what()<<endl;
            system("pause");
            continue;
            attempt++;
        }
    }
    if(!success){
        cout<<"Maximum Attempts Reached...";
        exit(0);
    }
}

I don't exactly know if its the structures that are the problem or I declared a string wrong because I've been looking for it for a while now and I can't seem to find the problem myself. The compiler didn't have any problems with the code. It compiled with no errors or warnings but the programs just doesn't run because of this error.

Is this code still salvageable? I don't know what's causing it.

Answer 1

Just change this

desc arr_description[8] = {0};

to this

desc arr_description[8];

and this

assets arr_assets[8] = {0};

to this

assets arr_assets[8];

Classes like assets and desc have their default constructors called by default. You don't have to initialise things unless you specifically want a particular initial value.

What your code was doing was using 0 to initialise a string , in that context 0 counts as a null pointer, and that's why you got the error message you did (ie 'basic_string::_M_construct null not valid' ). It should be clear that it makes no sense (in general) to initialise an object with 0 .

No doubt you saw = {0} in a context where it did make sense, but try to get out of the habit of copying code you don't fully understand, that rarely works out.

EDIT

Now here's an irony. As pointed out in the comments your code has another bug in that the pword array is not null terminated which makes assigning it to a string an error. A simple solution to this issue is to write

char pword[100] = {0};

because that would initialise the whole array to zeros and so your array would automatically be null terminated.

A different and perhaps better solution would be to change this code

if (pword[i] == 13) {
    break;
}

to this

if (pword[i] == 13) {
    pword[i] = 0;
    break;
}

which not only adds a null terminator in the right place, but also removes the 13 character from the end of your password. Obviously this also means you would have to change

string correctP = "Exer04\r";

to

string correctP = "Exer04";