why g++ shows “gets()” not declared ,even after including

Question

#include 
#include 
#include 

using namespace std;

int main()
{
    char str[30];
    gets(str);
}

when

Answer 1

gets was deprecated in C++11 and removed from C++14. If you are using GCC6.0 or newer then by default it uses C++14 and won't be available. Instead of using

main()
{
    char str[30];
    gets(str);
}

use

int main()
{
    std::string str;
    std::getline(cin, str);
}

Answer 2

gets is an unsafe function and is not supported by the C Standard any more.

Instead use fgets.

For example

#include <iostream>
#include <cstdio>
#include <cstring>

int main()
{
    char str[30];

    std::fgets(str, sizeof( str ), stdin );

    str[ std::strcspn( str, "\n" ) ] = '\0';

    //...
}