使用C ++的Xcode系统清除和“未使用表达式结果”错误

Question

While attempting to code a Tic Tac Toe game in Xcode to practice C++, I'm running into all sorts of issues which I have mostly fixed but I'm still having trouble understanding why I'm getting the following errors and how to properly fix them/avoid them.

Problem 1:

I've linked the curses library but I still get this error: conversion from string literal to 'char*' is deprecated .

#include <unistd.h>
#include <term.h>
void ClearScreen()
{
if (!cur_term)
{
    int result;
    setupterm( NULL, STDOUT_FILENO, &result );
    if (result <= 0) return;
}
putp( tigetstr( "clear" ) );
}  

Problem 2: I keep getting an Unused Entity Issue ( Expression result unused ).
(gridBox is a 2-d array of type char and player is type char as well, both global variables.)

    if (gridBox[0,0] == gridBox[1,0] && gridBox[1,0] == gridBox[2,0]) {

    if (player == 'X') {
        return 'X';
    }
    if (player == 'O') {
        return 'O';
    }
}

Problem 3: When I try changing the if statement in the last problem to...

    if (gridBox[0,0] == 'X' && gridBox[1,0] == 'X' && gridBox[2,0] == 'X') {
    return 'X';
}

I get this error: Comparison between pointer and integer ('char*' and 'int') .

This is driving me completely insane, please help.

Thank you all in advance!

Answer 1

1. Is just that: implicit conversion from a string literal, such as "clear" , to a pointer to non-const char, char* , used to be allowed for historical reasons but has been deprecated because it's very unsafe.
   This can cause some issues when interfacing with C libraries or old code, but is usually easily worked around.

   Replace it with a non-const array:

   char clear[] = "clear"; putp(tigetstr(clear));

2. Is caused by indexing the wrong way; a 2-D array is an array of arrays, and it is indexed like this:

   gridBox[0][0]

   The comma operator is used in some contexts if you want to evaluate two expressions in sequence and throw away the result of the first - a, b returns the value of b , so gridBox[0,0] is equivalent to gridBox[0] . It's quite rare in practice - so rare that compilers have started issuing warnings because it's almost never what you intend.

3. Since gridBox is an array of arrays of char , and since because of point 2) gridBox[0,0] is equivalent to gridBox[0] , gridBox[0] is an array of char.
   You can't compare arrays with == . Instead, they are implicitly converted to pointers to the array's first element, which are then used for comparison. Thus, the left hand side is a char* , and the right hand side is promoted to an int for comparison purposes, and those two can't be compared.
   If you fix your indexing problem, this problem will disappear at the same time.