Difference between const and define in php

Difference between const and define in php

If (...){ Const FOO = 'bar'; // invalid } But If (...){ Define ('foo', 'bar'); // valid } 4. const uses a normal constant name, and define can use an expression as the name. For example: Const FOO = 'bar '; For ($ I = 0; $ I <32; ++ $ I ){ Define ('bit _ '. $ I, 1 <$ I ); } 5. const can only accept static scalar, while define can use any expression. For example: Const BIT_5 = 1 <5; // invalid But Define ('bit _ 5', 1 <5); // valid 6. const is always case sensitive. however, define () can use the third parameter to define a case-insensitive constant, for example: Define ('foo', 'bar', true ); Echo FOO; // BAR Echo foo; // BAR As shown in the preceding example, const is easy to read. it is a language structure, while define is a method, which is much faster than define when defined by const. For which to use it, follow your own needs.