目录
一.实现string类
在前一节中我们了解了STL中string的部分接口,在这里我们实现一个自己的string类
当我们实现自己的string类时,名字会与库内的冲突,所以可以选择用命名空间解决
1.string的构造及析构
当我们在开空间的时候一般要多开一个用于存放\0
拷贝构造和赋值用传统方法写一般是开新空间,复制过去,释放旧空间,但是在这里我们使用现代写法,直接将空间交换过来使用
而在swap函数中使用::,是为了让他去调用库中的函数,而不是类中的
string(const char* str = "")
{
_size = strlen(str);
_capacity = _size;
_str = new char[_capacity + 1];
//strcpy(_str,str);不安全,会警告,可能无法实现功能,在后面主要使用strcpy_s
strcpy_s(_str, strlen(str) + 1, str);//c11标准
}
//深拷贝,若用编译器自动生成的为浅拷贝,析构时会出现问题
string(const string& s):_str(nullptr),_size(0),_capacity(0)
{
string tmp(s._str);
//his->swap(tmp);
swap(tmp);
}
void swap(string& s)
{
::swap(_str, s._str);
::swap(_size, s._size);
::swap(_capacity, s._capacity);
}
~string()
{
delete[] _str;
_str = nullptr;
_size = _capacity = 0;
}
string& operator=(string s)
{
//this->swap(s);
swap(s);
return *this;
}2.string类的遍历
对于string类的遍历我们可以通过[]+下标,迭代器,范围for语句遍历,以及c_str
所以我们需要自己定义迭代器,重载[]
typedef char* iterator;
iterator begin()
{
return _str;
}
iterator end()
{
return _str + _size;
}
char& operator[](size_t i)
{
assert(i < _size);
return _str[i];
}
const char& operator[](size_t i) const
{
assert(i < _size);
return _str[i];
}
const char* c_str()
{
return _str;
}3.string类的插入和删除
对于插入我们都要考虑的便是容量不够需要增容,同时也应该考虑字符串开始为空的情况,如果为空就给一个容量,否则就扩2倍
push_back的话我们只需要将字符加在末端即可
append将插入的字符串复制到原字符串末尾即可
+=对于单个push_back,字符串复用append
insert插入单个字符时,将字符从末尾开始向后移一位,将字符插入头即可,插入字符串时后移的位数变为插入字符串的长度
erase删除主要考虑两种情况,删除一部分和全部删完,全部删完比较简单,将删除的位置变为\0,将size变为pos即可,删除部分,将后面的字符前移覆盖
void push_back(char ch)
{
if (_size == _capacity)
{
size_t newcapacity = _capacity == 0 ? 2 : _capacity * 2;
reserve(newcapacity);
}
_str[_size] = ch;
++_size;
_str[_size] = '\0';
}
void append(const char* str)
{
size_t len = strlen(str);
if (_size + len > _capacity)
{
reserve(_size + len);
}
//strcpy(_str + _size, str);
strcpy_s(_str + _size, strlen(str) + 1, str);
_size += len;
}
string& operator+=(char ch)
{
this->push_back(ch);
return *this;
}
string& operator+=(const char* str)
{
this->append(str);
return *this;
}
string& insert(size_t pos, char ch)
{
assert(pos < _size);
if (_size == _capacity)
{
size_t newcapacity = _capacity == 0 ? 2 : _capacity * 2;
reserve(newcapacity);
}
int end = _size;
while (end >= (int)pos)
{
_str[end + 1] = _str[end];
--end;
}
_str[pos] = ch;
++_size;
return *this;
}
string& insert(size_t pos, const char* str)
{
assert(pos < _size);
size_t len = strlen(str);
if (_size + len > _capacity)
{
reserve(_size + len);
}
int end = _size;
while (end >= (int)pos)
{
_str[end + len] = _str[end];
--end;
}
for (size_t i = 0; i < len; ++i)
{
_str[pos++] = str[i];
}
_size += len;
return *this;
}
void erase(size_t pos, size_t len = npos)
{
assert(pos < _size);
if (len >= _size - pos)
{
_str[pos] = '\0';
_size = pos;
}
else
{
size_t i = pos + len;
while (i <= _size)
{
_str[i - len] = _str[i];
++i;
}
_size -= len;
}
}4.string类的空间处理
reserve比较简单,直接开出一段空间即可,而resize则需要考虑空间的缩小,缩小的话将给定位置变为\0,放大空间的话,reserve空间,然后将size后面的都填上给定的或默认字符
size_t size() const
{
return _size;
}
size_t capacity() const
{
return _capacity;
}
void reserve(size_t n)
{
if (n > _capacity)
{
char* tmp = new char[n + 1];
//strcpy(tmp, _str);
strcpy_s(tmp, strlen(_str) + 1, _str);
delete[] _str;
_str = tmp;
_capacity = n;
}
}
void resize(size_t n, char ch = '\0')
{
if (n < _size)
{
_str[n] = '\0';
_size = n;
}
else
{
if (n > _capacity)
{
reserve(n);
}
for (size_t i = _size; i < n; ++i)
{
_str[i] = ch;
}
_size = n;
_str[_size] = '\0';
}
}5.string类的查找
size_t find(char ch, size_t pos = 0)
{
for (size_t i = pos; i < _size; ++i)
{
if (_str[i] == ch)
{
return i;
}
}
return npos;
}
size_t find(const char* str, size_t pos = 0)
{
char* p = strstr(_str, str);
if (p == nullptr)
{
return npos;
}
else
{
return p - _str;
}
}6.string类的输出和输入
ostream& operator<<(ostream& out, const string& s)
{
for (size_t i = 0; i < s.size(); ++i)
{
cout << s[i];
}
return out;
}
//getline()只需要去掉if中的' '即可
istream& operator>>(istream& in, string& s)
{
while (1)
{
char ch;
ch = in.get();
if (ch == ' ' || ch == '\n')
{
break;
}
else
{
s += ch;
}
}
return in;
}7.string类的常用判断
bool operator<(const string& s)
{
int ret = strcmp(_str, s._str);
return ret < 0;
}
bool operator==(const string& s)
{
int ret = strcmp(_str, s._str);
return ret == 0;
}
bool operator<=(const string& s)
{
return *this < s || *this == s;
}
bool operator>(const string& s)
{
return !(*this <= s);
}
bool operator>=(const string& s)
{
return !(*this < s);
}
bool operator!=(const string& s)
{
return !(*this == s);
}二.整体代码
1.string.h
#pragma once
#include<iostream>
#include<assert.h>
using namespace std;
namespace wzyl
{
class string
{
public:
typedef char* iterator;
iterator begin()
{
return _str;
}
iterator end()
{
return _str + _size;
}
string(const char* str = "")
{
_size = strlen(str);
_capacity = _size;
_str = new char[_capacity + 1];
//strcpy(_str,str);不安全,会报错,无法实现功能,在后面主要使用strcpy_s
strcpy_s(_str, strlen(str) + 1, str);//c11标准
}
//深拷贝,若用编译器自动生成的为浅拷贝,析构时会出现问题
string(const string& s):_str(nullptr),_size(0),_capacity(0)
{
string tmp(s._str);
//his->swap(tmp);
swap(tmp);
}
void swap(string& s)
{
::swap(_str, s._str);
::swap(_size, s._size);
::swap(_capacity, s._capacity);
}
~string()
{
delete[] _str;
_str = nullptr;
_size = _capacity = 0;
}
string& operator=(string s)
{
//this->swap(s);
swap(s);
return *this;
}
size_t size() const
{
return _size;
}
size_t capacity() const
{
return _capacity;
}
char& operator[](size_t i)
{
assert(i < _size);
return _str[i];
}
const char& operator[](size_t i) const
{
assert(i < _size);
return _str[i];
}
const char* c_str()
{
return _str;
}
void reserve(size_t n)
{
if (n > _capacity)
{
char* tmp = new char[n + 1];
//strcpy(tmp, _str);
strcpy_s(tmp, strlen(_str) + 1, _str);
delete[] _str;
_str = tmp;
_capacity = n;
}
}
void resize(size_t n, char ch = '\0')
{
if (n < _size)
{
_str[n] = '\0';
_size = n;
}
else
{
if (n > _capacity)
{
reserve(n);
}
for (size_t i = _size; i < n; ++i)
{
_str[i] = ch;
}
_size = n;
_str[_size] = '\0';
}
}
void push_back(char ch)
{
if (_size == _capacity)
{
size_t newcapacity = _capacity == 0 ? 2 : _capacity * 2;
reserve(newcapacity);
}
_str[_size] = ch;
++_size;
_str[_size] = '\0';
}
void append(const char* str)
{
size_t len = strlen(str);
if (_size + len > _capacity)
{
reserve(_size + len);
}
//strcpy(_str + _size, str);
strcpy_s(_str + _size, strlen(str) + 1, str);
_size += len;
}
string& operator+=(char ch)
{
this->push_back(ch);
return *this;
}
string& operator+=(const char* str)
{
this->append(str);
return *this;
}
string& insert(size_t pos, char ch)
{
assert(pos < _size);
if (_size == _capacity)
{
size_t newcapacity = _capacity == 0 ? 2 : _capacity * 2;
reserve(newcapacity);
}
int end = _size;
while (end >= (int)pos)
{
_str[end + 1] = _str[end];
--end;
}
_str[pos] = ch;
++_size;
return *this;
}
string& insert(size_t pos, const char* str)
{
assert(pos < _size);
size_t len = strlen(str);
if (_size + len > _capacity)
{
reserve(_size + len);
}
int end = _size;
while (end >= (int)pos)
{
_str[end + len] = _str[end];
--end;
}
for (size_t i = 0; i < len; ++i)
{
_str[pos++] = str[i];
}
_size += len;
return *this;
}
void erase(size_t pos, size_t len = npos)
{
assert(pos < _size);
if (len >= _size - pos)
{
_str[pos] = '\0';
_size = pos;
}
else
{
size_t i = pos + len;
while (i <= _size)
{
_str[i - len] = _str[i];
++i;
}
_size -= len;
}
}
size_t find(char ch, size_t pos = 0)
{
for (size_t i = pos; i < _size; ++i)
{
if (_str[i] == ch)
{
return i;
}
}
return npos;
}
size_t find(const char* str, size_t pos = 0)
{
char* p = strstr(_str, str);
if (p == nullptr)
{
return npos;
}
else
{
return p - _str;
}
}
bool operator<(const string& s)
{
int ret = strcmp(_str, s._str);
return ret < 0;
}
bool operator==(const string& s)
{
int ret = strcmp(_str, s._str);
return ret == 0;
}
bool operator<=(const string& s)
{
return *this < s || *this == s;
}
bool operator>(const string& s)
{
return !(*this <= s);
}
bool operator>=(const string& s)
{
return !(*this < s);
}
bool operator!=(const string& s)
{
return !(*this == s);
}
private:
char* _str;
size_t _size;//有效字符个数
size_t _capacity;//能存多少有效字符,\0不是有效字符
static size_t npos;
};
size_t string::npos = -1;
ostream& operator<<(ostream& out, const string& s)
{
for (size_t i = 0; i < s.size(); ++i)
{
cout << s[i];
}
return out;
}
//getline()只需要去掉if中的' '即可
istream& operator>>(istream& in, string& s)
{
while (1)
{
char ch;
ch = in.get();
if (ch == ' ' || ch == '\n')
{
break;
}
else
{
s += ch;
}
}
return in;
}
void test_string1()
{
string s1("hello");
string s2;
cout << s1 << endl;
cout << s2 << endl;
cout << s1.c_str() << endl;
cout << s2.c_str() << endl;
//3种遍历方式
for (size_t i = 0; i < s1.size(); ++i)
{
s1[i] += 1;
cout << s1[i] << " ";
}
cout << endl;
string::iterator it = s1.begin();
while (it != s1.end())
{
*it -= 1;
cout << *it << " ";
++it;
}
cout << endl;
//范围for是由迭代器支持的,所以这段代码最后会被替换成迭代器
for (auto e : s1)
{
cout << e << " ";
}
cout << endl;
}
void test_string2()
{
string s1("hello");
s1.push_back(' ');
s1.push_back('w');
s1.push_back('o');
s1.push_back('r');
s1.push_back('l');
s1.push_back('d');
cout << s1 << endl;
s1.append("xxxxxxxxx");
cout << s1 << endl;
string s2;
s2 += "hello";
s2 += ' ';
s2 += "world";
cout << s2 << endl;
}
void test_string3()
{
string s1("hello");
s1.insert(1, 'x');
s1.insert(1, "xyz");
s1.insert(0, 'p');
cout << s1 << endl << endl;
string s2("hello");
s2.reserve(10);
cout << s2 << endl;
cout << s2.size() << endl;
cout << s2.capacity() << endl << endl;
s2.resize(10, 'x');
cout << s2 << endl;
cout << s2.size() << endl;
cout << s2.capacity() << endl << endl;
s2.resize(18, 'a');
cout << s2 << endl;
cout << s2.size() << endl;
cout << s2.capacity() << endl << endl;
s2.resize(2);
cout << s2 << endl;
cout << s2.size() << endl;
cout << s2.capacity() << endl;
}
void test_string4()
{
string s("helloworld");
s.erase(5, 2);
cout << s << endl;
s.erase(5, 4);
cout << s << endl;
string s1("abcdabcdef");
cout << s1.find("cde") << endl;
cout << s1.find("fgh") << endl;
}
void test_string5()
{
string s;
cin >> s;
cout << s << endl;
string s1(s);
cout << s1 << endl;
string s2 = s1;
cout << s2 << endl;
}
}2.string.cpp
#include "string.h"
int main()
{
wzyl::test_string1();
wzyl::test_string2();
wzyl::test_string3();
wzyl::test_string4();
wzyl::test_string5();
return 0;
}
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