C++ string类的模拟实现

#include "string.h" namespace Alen { const size_t string::npos = -1; void string::reserve(size_t newCapacity) { if (newCapacity > _capacity) { char* tmp = new char[newCapacity + 1]; // 多一个空间存'\0' strcpy(tmp, _str); delete[] _str; _str = tmp; _capacity = newCapacity; } } void string::clear() { _str[0] = '\0'; _size = 0; } void string::push_back(char c) { if (_size == _capacity) reserve(_capacity == 0 ? 4 : _capacity * 2); // 进行2倍扩容 _str[_size++] = c; _str[_size] = '\0'; // !!! } string& string::operator+=(char c) { push_back(c); return *this; } void string::append(const char* s) { size_t len = strlen(s); if (_size + len > _capacity) { reserve(_size + len > _capacity * 2 ? _size + len : _capacity * 2); } strcpy(_str + _size, s); _size += len; } string& string::operator+=(const char* s) { append(s); return *this; } void string::insert(size_t pos, char ch) { assert(pos <= _size); if (_size == _capacity) reserve(_capacity == 0 ? 4 : _capacity * 2); // 挪动数据 // end 是int类型，pos是size_t类型，比较会将end隐式类型转换成size_t // 当end为-1的（即pos为0）时候，就成为了size_t的最大值 //int end = _size; //while (end >= pos) //{ // _str[end + 1] = _str[end]; // --end; //} //_str[pos] = ch; //++_size; size_t end = _size + 1; while (end > pos) { _str[end] = _str[end - 1]; --end; } _str[pos] = ch; ++_size; } void string::insert(size_t pos, const char* s) { assert(pos <= _size); size_t len = strlen(s); if (_size + len > _capacity) reserve(_size + len > 2 * _capacity ? _size + len : 2 * _capacity); // 挪动数据 size_t end = _size + len; while (end > pos + len - 1) { _str[end] = _str[end - len]; } for (size_t i = 0; i < len; i++) { _str[pos + i] = s[i]; } } void string::erase(size_t pos, size_t len) { assert(pos < _size); if (len >= _size - pos) { _str[pos] = '\0'; _size = pos; } else { for (size_t i = pos + len; i <= _size; i++) { _str[i - len] = _str[i]; } _size -= len; } } size_t string::find(char c, size_t pos) { for (size_t i = pos; i < _size; i++) { if (_str[i] == c) { return i; } } return npos; } // 可以使用KMP、BM算法 size_t string::find(const char* s, size_t pos) { assert(pos < _size); const char* ptr = strstr(_str + pos, s); if (ptr == nullptr) { return npos; } else { return ptr - _str; } } string string::substr(size_t pos, size_t len) { assert(pos < _size); if (len > _size - pos) { len = _size - pos; } string sub; sub.reserve(len); for (size_t i = 0; i < len; i++) { sub += _str[pos + i]; } return sub; } bool operator<(const string& s1, const string& s2) { return strcmp(s1.c_str(), s2.c_str()) < 0; } bool operator<=(const string& s1, const string& s2) { return s1 < s2 || s1 == s2; } bool operator>(const string& s1, const string& s2) { return !(s1 <= s2); } bool operator>=(const string& s1, const string& s2) { return !(s1 < s2); } bool operator==(const string& s1, const string& s2) { return strcmp(s1.c_str(), s2.c_str()) == 0; } bool operator!=(const string& s1, const string& s2) { return !(s1 == s2); } ostream& operator<<(ostream& out, const string& s) { for (auto ch : s) { out << ch; } return out; } void IN(istream& in ,string& s, char option = '\n') { char ch; const int N = 256; char buff[N]; // 利用缓存区的思路，来减少string的扩容操作，增加效率 int i = 0; ch = in.get(); // = C语言的getc一个字符一个字符读 while (option == ' ' ? ch != ' ' && ch != '\n' : ch != option) { buff[i++] = ch; if (i == N - 1) { buff[i] = '\0'; s += buff; i = 0; } //s += ch; ch = in.get(); } if (i > 0) { buff[i] = '\0'; s += buff; } } istream& operator>>(istream& in, string& s) { s.clear(); /* char ch; //in >> ch; // 将 ' ' 与 '\n'作为分隔符，直接忽视不会读取 //while (ch != ' ' && ch != '\n') //{ // s += ch; // in >> ch; //} const int N = 256; char buff[N]; // 利用缓存区的思路，来减少string的扩容操作，增加效率 int i = 0; ch = in.get(); // = C语言的getc一个字符一个字符读 while (ch != ' ' && ch != '\n') { buff[i++] = ch; if (i == N - 1) { buff[i] = '\0'; s += buff; i = 0; } //s += ch; ch = in.get(); } if (i > 0) { buff[i] = '\0'; s += buff; } */ IN(in, s, ' '); return in; } istream& getline(istream& in, string& s, char delim) { s.clear(); IN(in, s, delim); return in; } }