__attribute__ 用于修饰 变量、结构体、函数、类型的关键字。
语法形式：
__attribute__((attribute1, attribute2, ...))
__attribute__((__attribute1__, __attribute2__, ...))常见用法
__attribute__((alias))__attribute__((always_inline))__attribute__((const))__attribute__((constructor(priority)))__attribute__((deprecated))__attribute__((malloc))__attribute__((nonull))__attribute__((unused))__attribute__((used))- 更多用法...
__attribute__((constructor)) 修饰的函数会在main函数之前调用。
__attribute__((constructor(priority))
priority 表示调用的优先级，是一个可选的整数。
priority 值越小优先级越高。
有 priority 修饰的优先级高于没有的。
priority 小于100的用作保留字段。
#include <stdio.h>
void my_constructor1(void) __attribute__((constructor));
void my_constructor2(void) __attribute__((constructor(102)));
void my_constructor3(void) __attribute__((constructor(103)));
void my_constructor1(void) /* This is the 3rd constructor */
{ /* function to be called */
printf("Called my_constructor1()\n");
}
void my_constructor2(void) /* This is the 1st constructor */
{ /* function to be called */
printf("Called my_constructor2()\n");
}
void my_constructor3(void) /* This is the 2nd constructor */
{ /* function to be called */
printf("Called my_constructor3()\n");
}
int main(void)
{
printf("Called main()\n");
}上面程序产生如下输出:
Called my_constructor2()
Called my_constructor3()
Called my_constructor1()
Called main()https://www.keil.com/support/man/docs/armclang_ref/armclang_ref_chr1383738546439.htm
如果函数、变量等，未被引用，用 __attrubute__((unused)) 修饰可以阻止编译器生成警告。
void test()
{
int a __attribute__((unused)) = 10;
}https://www.keil.com/support/man/docs/armclang_ref/armclang_ref_chr1393261558987.htm
用于修饰一个变量，在它的作用域结束后自动执行一个指定的方法。
The
cleanupattribute runs a function when the variable goes out of scope. This attribute can only be applied to auto function scope variables; it may not be applied to parameters or variables with static storage duration. The function must take one parameter, a pointer to a type compatible with the variable. The return value of the function (if any) is ignored.
static void stringCleanUp(__strong NSString **string) {
NSLog(@"%@", *string);
}
static void blockCleanUp(__strong void(^*block)(void)) {
NSLog(@"call block");
(*block)();
}
- (void)test {
__strong NSString *string __attribute__((cleanup(stringCleanUp), unused)) = @"peak";
void (^block)(void) __attribute__((cleanup(blockCleanUp), unused)) = ^ {
NSLog(@"this is a block implementation.");
};
}