update

Author: pangudashu

7/contant.md

@@ -0,0 +1,46 @@
+## 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);
+```

README.md

@@ -72,7 +72,7 @@
  * [7.7.3 引用计数](7/var.md)
  * [7.7.4 字符串操作](7/var.md)
  * [7.7.5 数组操作](7/var.md)
- * 7.8 常量
+ * [7.8 常量](7/constant.md)
  * 7.9 面向对象
  * 7.6.1 扩展中创建对象
  * 7.6.2 创建内部类