Example in Book Not Compiling(time function)

Question

I recently picked up a c++ book, " A Complete Guide to Programming in C++," and I can't seem to get an example to compile properly. I imagine it's a version issue, but I can't seem to find anything about this version of the 'time' function ever even working.

Has the 'time' function usage changed recently?

#include <iostream>
#include <string>
#include <iomanip>
#include <cctype>
#include <ctime>

using namespace std;

long timediff(void);
static string secret = "ISUS";
static long maxcount = 3, maxtime = 60;

bool getPassword()
{
    bool ok_flag = false;
    string word;
    int count = 0, time = 0;
    timediff();
    while (ok_flag != true && ++count <= maxcount)
    {
        cout << "\n\nInput the password: ";
        cin.sync();
        cin >> setw(20) >> word;
        time += timediff();
        if (time >= maxtime)
            break;
        if (word != secret)
            cout << "Invalid password!" << endl;
        else
            ok_flag = true;
    }
    return ok_flag;
}

long timediff()
{
    static long sec = 0;
    long oldsec = sec;
    time( &sec);
    return (sec - oldsec);
}

Yields the following error when I build...

1>d:\c++ training\learning\learning\source.cpp(39): error C2664: 'time_t time(time_t *const )': cannot convert argument 1 from 'long *' to 'time_t *const '
1>d:\c++ training\learning\learning\source.cpp(39): note: Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or function-style cast
1>Done building project "Learning.vcxproj" -- FAILED.

No. The example is just inherently broken. Discard that book. Choose another one from the [curated list](https://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list). — StoryTeller - Unslander Monica, Jan 08 '18 at 14:11
I didn't even have to read the abuse of `std::time`. The [using directive](https://stackoverflow.com/questions/1452721/why-is-using-namespace-std-considered-bad-practice) gave the quality of the book away. — StoryTeller - Unslander Monica, Jan 08 '18 at 14:18

score 7 · Accepted Answer · answered Jan 08 '18 at 14:15

The signature of std::time is

std::time_t time( std::time_t* arg );

Where std::time_t is defined as:

typedef /* unspecified */ time_t;

The book assumes long is the unspecified type. That is a poor lesson to any programmer. And you are learning it the hard way, because the typedef changes, but the code sample does not.

The whole point of a type alias like this is to abstract implementation details away. And allow you to write portable code. The assumption that the book makes about the alias is unfounded. And is a sign that the author should not be teaching anyone C++.

Great, that's all I needed to know! The book, for anyone curious, is [A Complete Guide to Programming in C++](https://www.amazon.com/Complete-Guide-Programming-Title-Demand/dp/0763718173) I've had this book for a few years, and seems it wasn't worth the read after all! — Alex Harris, Jan 09 '18 at 01:56

Example in Book Not Compiling(time function)

1 Answers1