Assertion failure in std::ispunct in a simple program - c++

Question

I'm using the book C++primer by Stanley B.Lippman and this error is caused by the solution of Excersise 3.2.3 test 3.10.It requires that write a program that reads a string of characters including punctuation and writes what was read but with the punctuation removed.
here's the code:
#include "stdafx.h"
#include <iostream>
#include <string>
#include <cctype>
using namespace std;
int main() {
string s;
cout << "Please input a string of characters including punctuation:" << endl;
getline(cin, s);
for (auto c : s) {
if (!ispunct(c))
cout << c;
}
cout << endl;
return 0;
}
when I run this code in Visual studio 2017 it shows this:
Debug Assertion failed.
Expression:c>=-1&&c<=255
For information on how your program can cause an assertion failure,see the Visual C++ documentation on asserts.
why it shows like this? I can't understand.

Answer 1

Although the assertion failure you get is due to a bad call to std::ispunct() (you should iterate over the string with an unsigned char), the proper solution would be to use std::iswpunct:
#include <iostream>
#include <string>
#include <locale>
#include <cwctype> // std::iswpunct
int main()
{
std::wstring s;
do {
std::wcout << "Please input a string of characters including punctuation:\n";
} while (!std::getline(std::wcin, s));
for (auto c : s) {
if (!std::iswpunct(c))
std::wcout << c;
}
std::wcout << std::endl;
}
On a Windows platform, the conjunction of std::wstring1 and std::iswpunct will let you handle Chinese characters right. Note that I assumed your system locale is "zh_CH.UTF-8". If it is not, you'll need to imbue your streams.
1) see this excellent answer about the difference between string and wstring.