Equality operators: == and !=

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Syntax

expression == expression
expression != expression

Remarks

The binary equality operators compare their operands for strict equality or inequality.

The equality operators, equal to (==) and not equal to (!=), have lower precedence than the relational operators, but they behave similarly. The result type for these operators is bool.

The equal-to operator (==) returns true if both operands have the same value; otherwise, it returns false. The not-equal-to operator (!=) returns true if the operands don't have the same value; otherwise, it returns false.

Operator keyword for !=

C++ specifies not_eq as an alternative spelling for !=. (There's no alternative spelling for ==.) In C, the alternative spelling is provided as a macro in the <iso646.h> header. In C++, the alternative spelling is a keyword; use of <iso646.h> or the C++ equivalent <ciso646> is deprecated. In Microsoft C++, the /permissive- or /Za compiler option is required to enable the alternative spelling.

Example

// expre_Equality_Operators.cpp
// compile with: /EHsc
#include <iostream>

using namespace std;

int main() {
   cout  << boolalpha
         << "The true expression 3 != 2 yields: "
         << (3 != 2) << endl
         << "The false expression 20 == 10 yields: "
         << (20 == 10) << endl;
}

Equality operators can compare pointers to members of the same type. In such a comparison, pointer-to-member conversions are performed. Pointers to members can also be compared to a constant expression that evaluates to 0.

See also

Expressions with binary operators
C++ built-in operators, precedence; and associativity
C relational and equality operators