C++简单String类的实现

发表于

这里给出了C++面试中String类的一种正确写法，我又添加了一些内容，给出完整的代码。其中赋值操作符的实现用到了一些小技巧，具体可以参见《Effective C++》：

  • 条款10：令operator=返回一个reference to *this（支持形如“x = y = z”的连锁赋值）
  • 条款11：在operator=中处理“自我赋值”（考虑异常安全性）
#include <iostream>
#include <vector>
using namespace std;

class String {
public:
    String() : data_(new char[1]) {
        *data_ = '\0';
    }

    String(const char *str) : data_(new char[strlen(str) + 1]) {
        strcpy(data_, str);
    }

    String(const String &rhs) : data_(new char[rhs.size() + 1]) {
        strcpy(data_, rhs.data_);
    }

    ~String() {
        delete [] data_;
    }

    String &operator=(String rhs) { // Effective C++
        swap(rhs);
        return *this;
    }

    char &operator[](size_t index) {
        return data_[index];
    }

    String &operator+=(const String &rhs) {
        strcat(data_, rhs.data_);
        return *this;
    }

    size_t size() const {
        return strlen(data_);
    }

    const char *c_str() const {
        return data_;
    }

    void swap(String &rhs) {
        std::swap(data_, rhs.data_);
    }
private:
    char *data_;
};

bool operator==(const String &lhs, const String &rhs) {
    return strcmp(lhs.c_str(), rhs.c_str()) == 0;
}

bool operator!=(const String &lhs, const String &rhs) {
    return !(lhs == rhs);
}

ostream &operator<<(ostream &os, const String &rhs) {
    os << rhs.c_str();
    return os;
}

String operator+(const String &lhs, const String &rhs) {
    String ret = lhs;
    ret += rhs;
    return ret;
}

int main()
{
    String s0 = "wor";
    s0 += "ld";

    String s1(s0);
    s0 = "hello";

    cout << s0 + ", " + s1 << endl;
    cout << (s0 == "hello") << endl;
    cout << s0[1] << endl;

    vector<String> v;
    v.push_back(s0);
    v.push_back(s1);

    for (auto s : v)
        cout << s << endl;

    return 0;
}
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