Gotcha

From Wikipedia, the free encyclopedia

A gotcha is a detrimental condition (usually of a contract or agreement) that is designed to sneak past the other party. For example, many "free" Credit Report sites have "gotchas" that automatically sign you up for a monthly credit report service unless you explicitly cancel. "Gotcha" is also a frequently used programming term.

Contents 1 Programming gotchas 2 Gotchas in the C programing language 2.1 Equality operator 2.2 Function calls 3 Gotchas in the C++ programing language 3.1 Initializer lists 4 External links 5 Gotchas

[edit] Programming gotchas

In programming, a gotcha is a feature of a system, a program or a programming language that works in the way it is documented but is counter-intuitive and almost invites mistakes because it is both enticingly easy to invoke and completely unexpected and/or unreasonable in its outcome.

[edit] Gotchas in the C programing language

[edit] Equality operator

The classic gotcha in C is the fact that

if (a=b) code;

is syntactically valid and sometimes even correct. It puts the value of b into a and then executes code if a is non-zero. What the programmer probably meant was

if (a==b) code;

which executes code if a and b are equal.

[edit] Function calls

In C and C++, function calls that need no arguments still require parentheses. If these are omitted the program will still compile, but will not produce the expected results. For example:

#include <iostream>
using namespace std;

int myfunc(){
  return 42;
}

int main (){
  cout << myfunc;
  return 0;
}

The program will only display the expected result (the string 42) if the form cout << myfunc(); is used. If the shown form cout << myfunc; is used, the address of the function myfunc is cast to a boolean value, and the program will instead display the string 1.

[edit] Gotchas in the C++ programing language

[edit] Initializer lists

In C++, it is the order of the class inheritance and of the member variables that determine the initialization order, not the order of an initializer list:

#include <iostream>

class CSomeClass
{
public:
    CSomeClass(int n)
    {
        std::cout << "CSomeClass constructor with value ";
        std::cout << n << std::endl;
    }
};

class CSomeOtherClass
{
public:
    CSomeOtherClass()    //In this example, despite the list order,
     : obj2(2), obj1(1)  //obj1 will be initialized before obj2.
    {
        //Do nothing.
    }
private:
    CSomeClass obj1;
    CSomeClass obj2;
};

int main(void)
{
    CSomeOtherClass obj;
    return 0;
}

[edit] External links

• from the HyperDictionary

[edit] Gotchas

Gotchas is a well known saltwater lure (artificial bait) that is used off of beaches, piers, bridges, jetties, etc. They come in a variety of colors and are pretty heavy and have treble hook on them. You can cast them long distances and you work the lure as fast as you can twitchin it to make it go back and forth. Some fish that you can catch with a Gotcha would be a spanish mackeral, Bluefish, Jack, etc. A gotcha really is a great saltwater lure.