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[手撕STL] string类
前言:
本文将string类中一些主要的函数模拟出来!
1.构造函数
通过缺省值构造函数,可以同时解决默认构造函数
string( const char* str="") :_str(new char[strlen(str)+1]) ,_size(strlen(str)) ,_capacity(strlen(str)) { strcpy(_str, str); }- 1
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2. 拷贝构造和赋值重载
基本写法
这里设计深浅拷贝,如果直接调用默认拷贝构造的话就是浅拷贝,当调用析构函数的时候就会崩溃,原因就是char*指针指向同一块空间了,所以我们必须采取深拷贝的方法,重新开辟一块空间
string(const string& s) { _str=new char[s._capacity+1]; _size = s._size; _capacity = s._capacity; strcpy(_str, s._str); } string& operator=(const string& s) { if (this != &s) { char* tmp = new char(s._capacity + 1); strcpy(tmp, s._str); delete[] _str; _size = s._size; _capacity = s._capacity; _str = tmp; } return *this; }- 1
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资本思维的写法(1)
通过调用构造函数完成拷贝构造!!
void swap(string& tmp) { std::swap(_str, tmp._str); std::swap(_size, tmp._size); std::swap(_capacity, tmp._capacity); } string(const string& s) { string tmp(s._str);//调用构造函数 swap(tmp); }- 1
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发挥到极致的资本思维的写法(2)
之前我们都是用的引用传参,现在我们用传值传参,我知道传值传参会生成一个拷贝,所以直接让s代替tmp打工
string& operator=(string s) { swap(s); return *this; } string& operator=(const string& s) { if (this != &s) { string tmp(s);//调用拷贝构造 swap(tmp); } return *this; }- 1
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3. 析构函数
~string() { _size = 0; _capacity = 0; _str = nullptr; delete[] _str; }- 1
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4. 内置函数实现(实现很常规)
size_t size() const { return _size; } char* c_str() { return _str; } size_t capacity() const { return _capacity; } const char& operator[](size_t pos) const { assert(pos < _size); return _str[pos]; } char& operator[](size_t pos) { assert(pos < _size); return _str[pos]; } void reserve(size_t n) { if (n > _capacity) { char* tmp = new char[n + 1]; strcpy(tmp, _str); delete[] _str; _str = tmp; _capacity = n; } } void push_back(char ch) { if (_size == _capacity) { reserve(_capacity == 0 ? 4 : _capacity * 2); } _str[_size] = ch; ++_size; _str[_size] = '\0'; } string& operator+=(char ch) { push_back(ch); return *this; } void append(const string& s) { if (_size + s._size > _capacity) { reserve(_size + s._size); } strcpy(_str + _size, s._str); _size += s._size; } string& operator+=(const string& s) { append(s); return *this; } string& insert(size_t pos, char ch) { assert(pos <= _size); if (_size+1 == _capacity) { reserve(_capacity == 0 ? 4 : _capacity * 2); } size_t end = _size + 1; while (end > pos) { _str[end] = _str[end - 1]; --end; } _str[pos] = ch; ++_size; return *this; } string& insert(size_t pos, const string& s) { assert(pos <= _size); if (_size+s._size == _capacity) { reserve(_size + s._size); } size_t end = _size + s._size; while (end > pos) { _str[end] = _str[end - s._size]; --end; } strncpy(_str + pos, s._str, s._size); _size+=s._size; return *this; } void erase(size_t pos, size_t len = npos) { assert(pos < _size); if (len == npos || pos + len >= _size) { _str[pos] = '\0'; _size = pos; } else { strcpy(_str + pos, _str + pos + len); _size -= len; } } void clear() { _str[0] = '\0'; _size = 0; } size_t find(char ch, size_t pos = 0) const { for (size_t i = pos; i < _size; ++i) { if (_str[i] == ch) return i; } return npos; } size_t find(const char* sub, size_t pos = 0) const { char* n = strstr(_str + pos, sub); if (n == nullptr) return npos; else return n - _str; } string substr(size_t pos, size_t len = npos) const { assert(pos < _size); size_t realLen = len; if (len == npos || pos + len > _size)//防止len过大 { realLen = _size - pos; } string sub; for (size_t i = 0; i < realLen; ++i) { sub += _str[pos + i]; } return sub; } bool operator>(const string& s) const { return strcmp(_str, s._str) > 0; } bool operator==(const string& s) const { return strcmp(_str, s._str) == 0; } bool operator>=(const string& s) const { return strcmp(_str, s._str) >= 0; } bool operator<=(const string& s) const { return strcmp(_str, s._str) <= 0; } bool operator<(const string& s) const { return strcmp(_str, s._str) < 0; } bool operator!=(const string& s) const { return !(*this==s); }- 1
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5. operator>>和operator<<
这里我并没有采用友元函数,直接通[]取到对应的字符
流插入这边做了一个小小的优化,就是我们每次输入都得+=,这用频繁的开辟空间效率较低,我们采用一个临时数组,将我们输入的这些字符都放到临时数组里然后统一+=到字符串中ostream& operator<<(ostream& out, const string& s) { for (size_t i = 0; i < s.size(); ++i) { out << s[i]; } return out; } istream& operator>>(istream& in, string& s) { s.clear(); char ch; ch = in.get(); const size_t N = 32; char buff[N]; size_t i = 0; while (ch != ' ' && ch != '\n') { buff[i++] = ch; if (i == N - 1) { buff[i] = '\0'; s += buff; i = 0; } ch = in.get(); } buff[i] = '\0'; s += buff; return in; }- 1
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完整代码
#pragma once #include#include using std::istream; using std::ostream; class string { public: typedef char* iterator; typedef const char* const_iterator; iterator begin() { return _str; } iterator end() { return _str+_size; } const_iterator begin() const { return _str; } const_iterator end() const { return _str + _size; } //string() // :_str(new char[1]) // ,_size(0) // ,_capacity(0) //{ // _str[0]='\0'; //} string( const char* str="") :_str(new char[strlen(str)+1]) ,_size(strlen(str)) ,_capacity(strlen(str)) { strcpy(_str, str); } //传统写法 //string(const string& s) //{ // _str=new char[s._capacity+1]; // _size = s._size; // _capacity = s._capacity; // strcpy(_str, s._str); //} //string& operator=(const string& s) //{ // if (this != &s) // { // char* tmp = new char(s._capacity + 1); // strcpy(tmp, s._str); // delete[] _str; // _size = s._size; // _capacity = s._capacity; // _str = tmp; // } // return *this; //} //老板思维(1) void swap(string& tmp) { std::swap(_str, tmp._str); std::swap(_size, tmp._size); std::swap(_capacity, tmp._capacity); } string(const string& s) { string tmp(s._str);//调用构造函数 swap(tmp); } //string& operator=(const string& s) //{ // if (this != &s) // { // string tmp(s); // swap(tmp); // } // return *this; //} //老板思维(2) //让s代替tmp打工 string& operator=(string s) { swap(s); return *this; } ~string() { _size = 0; _capacity = 0; _str = nullptr; delete[] _str; } size_t size() const { return _size; } char* c_str() { return _str; } size_t capacity() const { return _capacity; } const char& operator[](size_t pos) const { assert(pos < _size); return _str[pos]; } char& operator[](size_t pos) { assert(pos < _size); return _str[pos]; } void reserve(size_t n) { if (n > _capacity) { char* tmp = new char[n + 1]; strcpy(tmp, _str); delete[] _str; _str = tmp; _capacity = n; } } void push_back(char ch) { if (_size == _capacity) { reserve(_capacity == 0 ? 4 : _capacity * 2); } _str[_size] = ch; ++_size; _str[_size] = '\0'; } string& operator+=(char ch) { push_back(ch); return *this; } void append(const string& s) { if (_size + s._size > _capacity) { reserve(_size + s._size); } strcpy(_str + _size, s._str); _size += s._size; } string& operator+=(const string& s) { append(s); return *this; } string& insert(size_t pos, char ch) { assert(pos <= _size); if (_size+1 == _capacity) { reserve(_capacity == 0 ? 4 : _capacity * 2); } size_t end = _size + 1; while (end > pos) { _str[end] = _str[end - 1]; --end; } _str[pos] = ch; ++_size; return *this; } string& insert(size_t pos, const string& s) { assert(pos <= _size); if (_size+s._size == _capacity) { reserve(_size + s._size); } size_t end = _size + s._size; while (end > pos) { _str[end] = _str[end - s._size]; --end; } strncpy(_str + pos, s._str, s._size); _size+=s._size; return *this; } void erase(size_t pos, size_t len = npos) { assert(pos < _size); if (len == npos || pos + len >= _size) { _str[pos] = '\0'; _size = pos; } else { strcpy(_str + pos, _str + pos + len); _size -= len; } } void clear() { _str[0] = '\0'; _size = 0; } size_t find(char ch, size_t pos = 0) const { for (size_t i = pos; i < _size; ++i) { if (_str[i] == ch) return i; } return npos; } size_t find(const char* sub, size_t pos = 0) const { char* n = strstr(_str + pos, sub); if (n == nullptr) return npos; else return n - _str; } string substr(size_t pos, size_t len = npos) const { assert(pos < _size); size_t realLen = len; if (len == npos || pos + len > _size)//防止len过大 { realLen = _size - pos; } string sub; for (size_t i = 0; i < realLen; ++i) { sub += _str[pos + i]; } return sub; } bool operator>(const string& s) const { return strcmp(_str, s._str) > 0; } bool operator==(const string& s) const { return strcmp(_str, s._str) == 0; } bool operator>=(const string& s) const { return strcmp(_str, s._str) >= 0; } bool operator<=(const string& s) const { return strcmp(_str, s._str) <= 0; } bool operator<(const string& s) const { return strcmp(_str, s._str) < 0; } bool operator!=(const string& s) const { return !(*this==s); } private: char* _str; int _size; int _capacity; const static size_t npos = -1; }; ostream& operator<<(ostream& out, const string& s) { for (size_t i = 0; i < s.size(); ++i) { out << s[i]; } return out; } istream& operator>>(istream& in, string& s) { s.clear(); char ch; ch = in.get(); const size_t N = 32; char buff[N]; size_t i = 0; while (ch != ' ' && ch != '\n') { buff[i++] = ch; if (i == N - 1) { buff[i] = '\0'; s += buff; i = 0; } ch = in.get(); } buff[i] = '\0'; s += buff; return in; } - 1
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这就是程序员眼中的函数吗？（一）
- 原文地址：https://blog.csdn.net/m0_60565784/article/details/126350504
