## 7.8 常量 常量的具體實現前面章節已經介紹過，這里不再重復。PHP提供了很多用于常量注冊的宏，可以在擴展的`PHP_MINIT_FUNCTION()`中定義： ```c //注冊NULL常量 #define REGISTER_NULL_CONSTANT(name, flags) \ zend_register_null_constant((name), sizeof(name)-1, (flags), module_number) //注冊bool常量 #define REGISTER_BOOL_CONSTANT(name, bval, flags) \ zend_register_bool_constant((name), sizeof(name)-1, (bval), (flags), module_number) //注冊整形常量 #define REGISTER_LONG_CONSTANT(name, lval, flags) \ zend_register_long_constant((name), sizeof(name)-1, (lval), (flags), module_number) //注冊浮點型常量 #define REGISTER_DOUBLE_CONSTANT(name, dval, flags) \ zend_register_double_constant((name), sizeof(name)-1, (dval), (flags), module_number) //注冊字符串常量，str類型為char* #define REGISTER_STRING_CONSTANT(name, str, flags) \ zend_register_string_constant((name), sizeof(name)-1, (str), (flags), module_number) //注冊字符串常量，截取指定長度，str類型為char* #define REGISTER_STRINGL_CONSTANT(name, str, len, flags) \ zend_register_stringl_constant((name), sizeof(name)-1, (str), (len), (flags), module_number) ``` 除了上面這些還有`REGISTER_NS_XXX`系列的宏用于帶namespace的常量注冊，另外如果這些類型不能滿足需求，則可以通過`zend_register_constant(zend_constant *c)`注冊，比如常量類型為數組。 ```c PHP_MINIT_FUNCTION(mytest) { ... REGISTER_STRING_CONSTANT("MY_CONS_1", "this is a constant", CONST_CS | CONST_PERSISTENT); } ``` ```php echo MY_CONS_1; =========[output]========= this is a constant ``` 如果在擴展中需要用到其他擴展或內核定義的常量，則可以通過以下函數獲取常量的值： ```c ZEND_API zval *zend_get_constant(zend_string *name); ZEND_API zval *zend_get_constant_str(const char *name, size_t name_len); ```