📅  最后修改于: 2020-12-15 04:23:45             🧑  作者: Mango
函数对象是专门设计用于与函数语法相似的语法的对象。 std ::函数的实例可以存储,复制和调用任何Callable目标-函数,lambda表达式,绑定表达式或其他函数对象,以及指向成员函数的指针和指向数据成员的指针。
以下是std :: 函数的声明。
template
class function;
template< class R, class... Args >
class function
R-结果类型。
arguments_type-如果sizeof …(Args)== 1并且T是Args中的第一个也是唯一的类型,则为T。
在下面的std :: 函数示例中。
#include
#include
struct Foo {
Foo(int num) : num_(num) {}
void print_add(int i) const { std::cout << num_+i << '\n'; }
int num_;
};
void print_num(int i) {
std::cout << i << '\n';
}
struct PrintNum {
void operator()(int i) const {
std::cout << i << '\n';
}
};
int main() {
std::function f_display = print_num;
f_display(-9);
std::function f_display_42 = []() { print_num(42); };
f_display_42();
std::function f_display_31337 = std::bind(print_num, 31337);
f_display_31337();
std::function f_add_display = &Foo::print_add;
const Foo foo(314159);
f_add_display(foo, 1);
std::function f_num = &Foo::num_;
std::cout << "num_: " << f_num(foo) << '\n';
using std::placeholders::_1;
std::function f_add_display2= std::bind( &Foo::print_add, foo, _1 );
f_add_display2(2);
std::function f_add_display3= std::bind( &Foo::print_add, &foo, _1 );
f_add_display3(3);
std::function f_display_obj = PrintNum();
f_display_obj(18);
}
样本输出应该像这样-
-9
42
31337
314160
num_: 314159
314161
314162
18
Sr.No. | Member functions | Definition |
---|---|---|
1 | (constructor) | It is used to construct a new std::function instance |
2 | (destructor) | It is used to destroy a std::function instance |
3 | operator= | It is used to assign a new target |
4 | swap | It is used to swap the contents |
5 | assign | It is used to assign a new target |
6 | operator bool | It is used to check if a valid target is contained |
7 | operator() | It is used to invoke the target |
Sr.No. | Non-member functions | Definition |
---|---|---|
1 | std::swap | It specializes the std::swap algorithm |
2 | operator== operator!= | It compares an std::function with nullptr |
Sr.No. | Operator classes | Definition |
---|---|---|
1 | bit_and | It is a bitwise AND function object class |
2 | bit_or | It is a bitwise OR function object class |
3 | bit_xor | It is a bitwise XOR function object class |
3 | divides | It is a division function object class |
4 | equal_to | It is a function object class for equality comparison |
5 | greater | It is a function object class for greater-than inequality comparison |
6 | greater_equal | It is a function object class for greater-than-or-equal-to comparison |
7 | less | It is a function object class for less-than inequality comparison |
8 | less_equal | It is a function object class for less-than-or-equal-to comparison |
9 | logical_and | It is a logical AND function object class |
10 | logical_not | It is a logical NOT function object class |
11 | logical_or | It is a logical OR function object class |
12 | minus | It is a subtraction function object class |
13 | modulus | It is a modulus function object class |
14 | multiplies | It is a multiplication function object class |
15 | negate | It is a negative function object class |
16 | not_equal_to | It is a function object class for non-equality comparison |
17 | plus | It is an addition function object class |