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一、string转char*

1、c_str()方法

string str="world";
const char* p = str.c_str();// 加const或等号右边用char*

2、data()方法

string str = "hello";
const char* p = str.data();

3、copy()方法

string str="qweqwe";
char data[30];
str.copy(data,3,0);// 0表示复制开始的位置，3代表复制的字符个数

二、char* 转string

string s;
char *p = "hello";
s = p;

三、string的常用方式

1、创建和初始化

#include <iostream>
#include <string>

int main() {
    std::string str1; // 默认构造函数，创建一个空字符串
    std::string str2("Hello, World!"); // 使用C字符串初始化
    std::string str3 = "Hello, C++!"; // 使用字符串字面量初始化
    std::string str4(str2); // 拷贝构造函数
    std::string str5(10, 'A'); // 创建一个包含10个'A'字符的字符串

    std::cout << "str1: " << str1 << std::endl;
    std::cout << "str2: " << str2 << std::endl;
    std::cout << "str3: " << str3 << std::endl;
    std::cout << "str4: " << str4 << std::endl;
    std::cout << "str5: " << str5 << std::endl;

    return 0;
}

2、访问和修改字符

#include <iostream>
#include <string>

int main() {
    std::string str = "Hello, World!";
    
    // 访问字符串中的字符
    char firstChar = str[0];
    char lastChar = str.at(str.size() - 1);

    std::cout << "First character: " << firstChar << std::endl;
    std::cout << "Last character: " << lastChar << std::endl;

    // 修改字符串中的字符
    str[7] = 'C';
    str.at(8) = '+';

    std::cout << "Modified string: " << str << std::endl;

    return 0;
}

3、字符串的连接

#include <iostream>
#include <string>

int main() {
    std::string str1 = "Hello, ";
    std::string str2 = "World!";
    
    // 使用加号操作符连接字符串
    std::string str3 = str1 + str2;
    std::cout << "Concatenated string: " << str3 << std::endl;

    // 使用append函数连接字符串
    str1.append(str2);
    std::cout << "Appended string: " << str1 << std::endl;

    return 0;
}

4、查找和替换

#include <iostream>
#include <string>

int main() {
    std::string str = "Hello, World!";
    
    // 查找子串
    std::size_t pos = str.find("World");
    if (pos != std::string::npos) {
        std::cout << "'World' found at position: " << pos << std::endl;
    } else {
        std::cout << "'World' not found" << std::endl;
    }

    // 提取子串
    std::string subStr = str.substr(7, 5);
    std::cout << "Substring: " << subStr << std::endl;

    // 替换子串
    str.replace(7, 5, "C++");
    std::cout << "Replaced string: " << str << std::endl;

    return 0;
}

5、字符串比较

#include <iostream>
#include <string>

int main() {
    std::string str1 = "Hello";
    std::string str2 = "World";
    std::string str3 = "Hello";

    // 使用比较操作符
    if (str1 == str3) {
        std::cout << "str1 is equal to str3" << std::endl;
    }
    if (str1 != str2) {
        std::cout << "str1 is not equal to str2" << std::endl;
    }

    // 使用compare函数
    if (str1.compare(str2) < 0) {
        std::cout << "str1 is less than str2" << std::endl;
    } else if (str1.compare(str2) > 0) {
        std::cout << "str1 is greater than str2" << std::endl;
    } else {
        std::cout << "str1 is equal to str2" << std::endl;
    }

    return 0;
}

6、字符串长度和清空

#include <iostream>
#include <string>

int main() {
    std::string str = "Hello, World!";
    
    // 获取字符串长度
    std::cout << "Length: " << str.size() << std::endl;
    std::cout << "Length: " << str.length() << std::endl;

    // 检查字符串是否为空
    if (!str.empty()) {
        std::cout << "String is not empty" << std::endl;
    }

    // 清空字符串
    str.clear();
    if (str.empty()) {
        std::cout << "String is empty after clear" << std::endl;
    }

    return 0;
}

四、char字节操作

1、4字节转int

#include <iostream>
#include <cstdint>

// 枚举类型用于表示字节序
enum Endianness {
    LITTLE_ENDIAN,
    BIG_ENDIAN
};

// 检查系统的字节序
Endianness checkSystemEndianness() {
    uint32_t value = 0x1;
    char *bytePtr = reinterpret_cast<char*>(&value);
    return bytePtr[0] == 1 ? LITTLE_ENDIAN : BIG_ENDIAN;
}

// 将 char[4] 转换为 int 的函数
int charArrayToInt(const char buffer[4], Endianness endianness) {
    uint32_t value = 0;
    if (endianness == LITTLE_ENDIAN) {
        value = static_cast<uint8_t>(buffer[0]) |
                (static_cast<uint8_t>(buffer[1]) << 8) |
                (static_cast<uint8_t>(buffer[2]) << 16) |
                (static_cast<uint8_t>(buffer[3]) << 24);
    } else { // BIG_ENDIAN
        value = static_cast<uint8_t>(buffer[3]) |
                (static_cast<uint8_t>(buffer[2]) << 8) |
                (static_cast<uint8_t>(buffer[1]) << 16) |
                (static_cast<uint8_t>(buffer[0]) << 24);
    }
    return static_cast<int>(value);
}

int main() {
    // 示例字节数组
    char buffer[4] = {0x01, 0x02, 0x03, 0x04};

    // 检查系统字节序
    Endianness systemEndianness = checkSystemEndianness();
    std::cout << "系统字节序: " << (systemEndianness == LITTLE_ENDIAN ? "小端序" : "大端序") << std::endl;

    // 将 char[4] 转换为 int
    int value = charArrayToInt(buffer, systemEndianness);
    std::cout << "转换后的整数: " << value << std::endl;

    return 0;
}

• 大端序（Big Endian）：最高有效字节（Most Significant Byte, MSB）存储在最低地址。
• 小端序（Little Endian）：最低有效字节（Least Significant Byte, LSB）存储在最低地址。