Compiler says logical and is undefined identifier

Question

I learned c++ on a mac, and have recently transferred over to windows 7. I downloaded the windows v7.1 sdk and ran the installer. Its the .net 4 dependent version of the sdk, and I have .net 4 installed.

I am using the command line because I prefer using it, I did that with the gcc compiler on the mac and I got pretty good at it considering I am pretty new to programing.

I have been using the v7.1 sdk developer command prompt because it sets up the environment variables using the SetEnv batch file.

The compiler is obviously the cl.exe compiler from Microsoft.

I ran the typical and very simple hello world program, including a getchar() at the end to let me actually see the program, something new since mac didn't require that. And the getchar worked fine, the program compiled and ran fine.

The problem showed up when I tried compiling some source code I wrote on the mac. Which compiled fine on the mac by the way. It started throwing up some really weird errors, such as telling me that the logical 'and' operator is an undefined identifier. Now I could be the stupid one here, but from my understanding the and operator is NOT an identifier, it's an operator.

So I decided to narrow down the problem by writing a very simple program that makes use of one if statement and one else statement and the 'and' operator and see what happens. Below is the code I tried to compile:

//hello, this is a test

#include <iostream>

int main()

{

    char end;
    int a = 0, b = 0;

    std::cout << "If the variable a is larger than 10 and variable b is less than a, then b will be subtracted from a, else they are added.\n";
    std::cout << "Enter a number for variable a\n";
    std::cin >> a;
    std::cout << "Now enter a number for variable b\n";
    std::cin >> b;

    if (a>10 and b<a) a - b;
    else a+b;
    std::cout << "The value of a is: " <<a;

    std::cout << "Press any key to exit";
    end = getchar();
    return 0;
}

---

And this is the command I used to compile the program

cl /EHsc main.cpp

And last but certainly not least, the list of errors that this program raised, why these errors are here I am not sure. It just doesn't make any sense to me.

main.cpp

error C2146: syntax error : missing ')' before identifier 'and'

error C2065: 'and' : undeclared identifier

error C2146: syntax error : missing ';' before identifier 'b'

error C2059: syntax error : ')'

error C2146: syntax error : missing ';' before identifier 'a'

warning C4552: '<' : operator has no effect; expected operator with side-effect

warning C4552: '-' : operator has no effect; expected operator with side-effect

error C2181: illegal else without matching if

warning C4552: '+' : operator has no effect; expected operator with side-effect

---

Every last one of these errors is weird. I have never encountered it before, and I have never asked a question before because I have always been able to find my answer without asking, but on this one I am really stumped.

Answer 1

This is a bug (a feature) in Microsoft Visual C++ compiler - it does not support keywords and, and_eq, bitand, bitor, compl, not, not_eq, or, or_eq, xor, xor_eq. You should use more commonly used operators like && instead of and, || instead of or etc. Equivalence table:

+--------+-------+
| and    |  &&   |
| and_eq |  &=   |
| bitand |  &    |
| bitor  |  |    |
| compl  |  ~    |
| not    |  !    |
| not_eq |  !=   |
| or     |  ||   |
| or_eq  |  |=   |
| xor    |  ^    |
| xor_eq |  ^=   |
+--------+-------+

Unlike C++, C does not provide those keywords, instead it provides a header <iso646.h> with a set of macros with those names that expand to those logical operators. It was done to provide support for machines that did not have required characters on a keyboard back in the past.

Because C++ tries to avoid macros as much as possible, C++ header equivalent <ciso646> does not define any macros, instead those are provided as builtin keywords.

As was noted here, newer versions of MSVC might add some support for this, but you should know that those "altenative operators" are rarely used. I advise you to stick with original C syntax.

Answer 2

These alternative operators are defined in the <iso646.h> header as macros in Visual C++ implementation. They are built into the C++ language with others. Either include this header:

#include <iso646.h>

or compile with the /permissive- compiler switch when using the Visual C++ compiler. You don't need to include the above header when compiling with GCC. The GCC implementation seems to respect the alternative operators representation reference which states:

The same words are defined in the C programming language in the include file <iso646.h> as macros. Because in C++ these are built into the language, the C++ version of <iso646.h>, as well as <ciso646>, does not define anything.

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