蓝桥ROS机器人之现代C++学习笔记第 9 章其他杂项

zhangrelay

发布于 2022-04-29 19:55:41

5280

9.1 新类型

`long long int`

64位

在本文中，我们将讨论 C++ 中的 long long int 数据类型。 C++ 中的 long long int 数据类型用于存储 64 位整数。它是存储整数值的最大数据类型之一，不像 unsigned long long int 正数和负数。

long long int 数据类型的一些属性是：

作为有符号数据类型，它可以存储正值和负值。采用 64 位大小，其中 1 位用于存储整数的符号。可以存储在 long long int 数据类型中的最大整数值通常是 9、223、372、036、854、775、807，大约为 263 – 1（但取决于编译器）。 long long int 中可以存储的最大值作为常量存储在 <climits> 头文件中。其值可用作 LLONG_MAX。可以存储在 long long int 数据类型中的最小整数值通常为 –9、223、372、036、854、775、808，大约为 –263（但取决于编译器）。在数据类型上溢或下溢的情况下，该值将被环绕。例如，如果 –9、223、372、036、854、775、808 存储在 long long int 数据类型中并从中减去 1，则该变量中的值将等于 9、223、372、036 , 854, 775, 807. 同样，在溢出的情况下，该值将四舍五入为 –9, 223, 372, 036, 854, 775, 808。下面是在 C++ 中获取可以存储在 long long int 中的最大值的程序：

// C++ program to illustrate the maximum
// value that can be stored in long long int
#include <climits>
#include <iostream>
using namespace std;

// Driver Code
int main()
{
	// From the constant of climits
	// header file
	long long int valueFromLimits = LLONG_MAX;
	cout << "Value from climits "
		<< "constant (maximum): ";
	cout << valueFromLimits
		<< "\n";

	valueFromLimits = LLONG_MIN;
	cout << "Value from climits "
		<< "constant (minimum): ";
	cout << valueFromLimits
		<< "\n";

	return 0;
}

9.2 noexcept 的修饰和操作

#include <iostream>

void may_throw() {
    throw true;
}
auto non_block_throw = []{
    may_throw();
};
void no_throw() noexcept {
    return;
}

auto block_throw = []() noexcept {
    no_throw();
};

int main()
{
    std::cout << std::boolalpha
    << "may_throw() noexcept? " << noexcept(may_throw()) << std::endl
    << "no_throw() noexcept? " << noexcept(no_throw()) << std::endl
    << "lmay_throw() noexcept? " << noexcept(non_block_throw()) << std::endl
    << "lno_throw() noexcept? " << noexcept(block_throw()) << std::endl;
    
    try {
        may_throw();
    } catch (...) {
        std::cout << "exception captured from my_throw()" << std::endl;
    }
    
    try {
        non_block_throw();
    } catch (...) {
        std::cout << "exception captured from non_block_throw()" << std::endl;
    }
    
    try {
        block_throw();
    } catch (...) {
        std::cout << "exception captured from block_throw()" << std::endl;
    }
}

// noexceptOperator.cpp

#include <iostream>
#include <array>
#include <vector>

class NoexceptCopy{
public:
  std::array<int, 5> arr{1, 2, 3, 4, 5};             // (2)
};

class NonNoexceptCopy{
public:
  std::vector<int> v{1, 2, 3, 4 , 5};                // (3)
};

template <typename T> 
T copy(T const& src) noexcept(noexcept(T(src))){     // (1)
  return src; 
}

int main(){
    
    NoexceptCopy noexceptCopy;
    NonNoexceptCopy nonNoexceptCopy;
    
    std::cout << std::boolalpha << std::endl;
    
    std::cout << "noexcept(copy(noexceptCopy)): " <<            // (4)
                  noexcept(copy(noexceptCopy)) << std::endl;
                   
    std::cout << "noexcept(copy(nonNoexceptCopy)): " <<         // (5)
                  noexcept(copy(nonNoexceptCopy)) << std::endl;

    std::cout << std::endl;

}

9.3 字面量

#include <iostream>
#include <string>

std::string operator"" _wow1(const char *wow1, size_t len) {
    return std::string(wow1)+"woooooooooow, amazing";
}

std::string operator""_wow2 (unsigned long long i) {
    return std::to_string(i)+"woooooooooow, amazing";
}

int main() {
    std::string str = R"(C:\\File\\To\\Path)";
    std::cout << str << std::endl;
    
    int value = 0b1001010101010;
    std::cout << value << std::endl;
    
    
    auto str2 = "abc"_wow1;
    auto num = 1_wow2;
    std::cout << str2 << std::endl;
    std::cout << num << std::endl;
    return 0;
}

9.4 内存对齐

#include <iostream>

struct Storage {
    char      a;
    int       b;
    double    c;
    long long d;
};

struct alignas(std::max_align_t) AlignasStorage {
    char      a;
    int       b;
    double    c;
    long long d;
};

int main() {
    std::cout << alignof(Storage) << std::endl;
    std::cout << alignof(AlignasStorage) << std::endl;
    return 0;
}