## 7.8 常量 常量的具体实现前面章节已经介绍过，这里不再重复。PHP提供了很多用于常量注册的宏，可以在扩展的`PHP_MINIT_FUNCTION()`中定义： ```c //注册NULL常量 #define REGISTER_NULL_CONSTANT(name, flags) \ zend_register_null_constant((name), sizeof(name)-1, (flags), module_number) //注册bool常量 #define REGISTER_BOOL_CONSTANT(name, bval, flags) \ zend_register_bool_constant((name), sizeof(name)-1, (bval), (flags), module_number) //注册整形常量 #define REGISTER_LONG_CONSTANT(name, lval, flags) \ zend_register_long_constant((name), sizeof(name)-1, (lval), (flags), module_number) //注册浮点型常量 #define REGISTER_DOUBLE_CONSTANT(name, dval, flags) \ zend_register_double_constant((name), sizeof(name)-1, (dval), (flags), module_number) //注册字符串常量，str类型为char* #define REGISTER_STRING_CONSTANT(name, str, flags) \ zend_register_string_constant((name), sizeof(name)-1, (str), (flags), module_number) //注册字符串常量，截取指定长度，str类型为char* #define REGISTER_STRINGL_CONSTANT(name, str, len, flags) \ zend_register_stringl_constant((name), sizeof(name)-1, (str), (len), (flags), module_number) ``` 除了上面这些还有`REGISTER_NS_XXX`系列的宏用于带namespace的常量注册，另外如果这些类型不能满足需求，则可以通过`zend_register_constant(zend_constant *c)`注册，比如常量类型为数组。 ```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 ``` 如果在扩展中需要用到其他扩展或内核定义的常量，则可以通过以下函数获取常量的值： ```c ZEND_API zval *zend_get_constant(zend_string *name); ZEND_API zval *zend_get_constant_str(const char *name, size_t name_len); ```