思考：如何在目标字符串中查找是否存在指定的字符串？
String s = "D.T.Software";
int pos = s.indexOf("Software");字符串类中的新功能
| 成员函数 | 功能描述 |
| indexOf(s) | 查找字串在字符串中的位置 |
| remove(s) | 将字符串中的字串 s 删除 |
| operator-(s) | 定义字符串减法 |
| replace(s, t) | 将字符串中的字串 s 替换为 t |
| sub(i, len) | 从字符串中创建子串 |
字串查找（KMP 算法的直接运用）
- int indexOf(const char *s) const;
- int indexOf(const String &s) const;
int String::indexOf(const char *s) const
{
return kmp(m_str, s);
}
int String::indexOf(const String &s) const
{
return kmp(m_str, s.m_str);
}在字符串中将指定的子串删除
- String &remove(const char *s);
- String &remove(const String &s);
- 根据 KMP 在目标字符串中查找字串的位置
- 通过字串位置和字串长度进行删除
String &String::remove(size_t i, size_t len)
{
if (i < m_length)
{
size_t n = i;
size_t m = i + len;
while ((n < m) && (m < m_length))
{
m_str[n++] = m_str[m++];
}
m_str[n] = '\0';
m_length = n;
}
return *this;
}
String &String::remove(const char *s)
{
return remove(indexOf(s), s ? strlen(s) : 0);
}
String &String::remove(const String &s)
{
return remove(indexOf(s), s.length());
}字符串的减法操作定义 (operator -)
使用 remove 实现字符串的减法操作
- 字符串自身不被修改
- 返回产生的新串
String String::operator - (const char *s) const
{
return String(*this).remove(s);
}
String String::operator - (const String &s) const
{
return String(*this).remove(s);
}
String &String::operator -= (const char *s)
{
return remove(s);
}
String &String::operator -= (const String &s)
{
return remove(s);
}字符串的子串替换
- String &replace(const char t, const char s);
- String &replace(const String &t, const char *s);
- String &replace(const char *t, const String &s);
- String &replace(const String &t, const String &s);
String &String::replace(const char *t, const char* s)
{
int index = indexOf(t);
if (index >= 0)
{
remove(t);
insert(index, s);
}
return *this;
}
String &String::replace(const String &t, const char *s)
{
return replace(t.str(), s);
}
String &String::replace(const char *t, const String &s)
{
return replace(t, s.str());
}
String &String::replace(const String &t, const String &s)
{
return replace(t.str(), s.str());
}从字符串中创建字串
String sub(int i, int len) const
- 以 i 为起点提取长度为 len 的字串
- 字串提取不会改变字符串本身的状态
String String::sub(size_t i, size_t len) const
{
String ret;
if (i < m_length)
{
if (len + i > m_length) len = m_length - i;
char *str = reinterpret_cast(malloc(len + 1));
if (str != nullptr)
{
strncpy(str, m_str + i, len);
str[len] = '\0';
ret = str;
}
free(str);
}
else
{
THROW_EXCEPTION(IndexOutOfBoundsException, "Parameter i is Invalid ...");
}
return ret;
} 编程实验：新成员函数的实现 [最终版]
文件：DTString.h
#ifndef STRING_H
#define STRING_H
#include "Exception.h"
#include "Object.h"
#include
namespace DTLib
{
class String
{
public:
String();
String(const String &s);
String(const char* s);
size_t length() const;
const char *str() const;
bool startWith(const char *s) const;
bool startWith(const String &s) const;
bool endOf(const char *s) const;
bool endOf(const String &s) const;
String &insert(size_t i, const char *s);
String &insert(size_t i, const String &s);
String &trim();
int indexOf(const char *s) const;
int indexOf(const String &s) const;
String &remove(size_t i, size_t len);
String &remove(const char *s);
String &remove(const String &s);
String &replace(const char *t, const char* s);
String &replace(const String &t, const char *s);
String &replace(const char *t, const String &s);
String &replace(const String &t, const String &s);
String sub(size_t i, size_t len) const;
bool operator == (const char *s) const;
bool operator == (const String &s) const;
bool operator != (const char *s) const;
bool operator != (const String &s) const;
bool operator > (const char *s) const;
bool operator > (const String &s) const;
bool operator < (const char *s) const;
bool operator < (const String &s) const;
bool operator >= (const char *s) const;
bool operator >= (const String &s) const;
bool operator <= (const char *s) const;
bool operator <= (const String &s) const;
String operator + (const char *s) const;
String operator + (const String &s) const;
String &operator += (const char *s);
String &operator += (const String &s);
String operator - (const char *s) const;
String operator - (const String &s) const;
String &operator -= (const char *s);
String &operator -= (const String &s);
String &operator = (const char c);
String &operator = (const char *s);
String &operator = (const String &s);
char &operator[] (size_t i);
char operator[] (size_t i) const;
~String();
protected:
char *m_str = nullptr;
size_t m_length = 0;
static int *make_pmt(const char *p);
static int kmp(const char *s, const char *p);
};
}
#endif // STRING_H 文件：DTString.cpp
#include "DTString.h"
#include
#include
namespace DTLib
{
int *String::make_pmt(const char *p) // O(m)
{
size_t len = strlen(p);
int *ret = static_cast(malloc(sizeof(int) * len));
if (ret != nullptr)
{
int ll = 0;
ret[0] = 0;
for (size_t i=1; i 0) && (p[i] != p[ll]))
{
ll = ret[ll - 1];
}
if (p[i] == p[ll])
{
++ll;
}
ret[i] = ll;
}
}
return ret;
}
int String::kmp(const char *s, const char *p) // O(m + n)
{
int ret = -1;
int sl = strlen(s);
int pl = strlen(p);
int *pmt = make_pmt(p); // O(m)
if ((pmt != nullptr) && (0 < pl) &&(pl <= sl))
{
for (int i=0, j = 0; i < sl; ++i) // O(n)
{
while ((j > 0) && (s[i] != p[j]))
{
j = pmt[j - 1];
}
if (s[i] == p[j])
{
++j;
}
if (j == pl)
{
ret = i + 1 - pl;
break;
}
}
}
free(pmt);
return ret;
}
String::String() : String("")
{
}
String::String(const String &s) : String(s.m_str)
{
}
String::String(const char* s)
{
char* str = strdup(s);
if (str != nullptr)
{
m_str = str;
m_length = strlen(str);
}
else
{
THROW_EXCEPTION(NoEnoughMemoryException, "No enogh memory to create str object ...");
}
}
size_t String::length() const
{
return m_length;
}
const char *String::str() const
{
return m_str;
}
bool String::startWith(const char *s) const
{
bool ret = (s != nullptr);
if (ret)
{
size_t len = strlen(s);
ret = (m_length > len) && (strncmp(m_str, s, len) == 0);
}
return ret;
}
bool String::startWith(const String &s) const
{
return startWith(s.str());
}
bool String::endOf(const char *s) const
{
bool ret = (s != nullptr);
if (ret)
{
size_t len = strlen(s);
char *str = m_str + (m_length - len);
ret = (m_length > len) && (strncmp(str, s, len) == 0);
}
return ret;
}
bool String::endOf(const String &s) const
{
return endOf(s.str());
}
String &String::insert(size_t i, const char *s)
{
if (i <= m_length)
{
if ((s != nullptr) || s[0] != '\0')
{
size_t len = strlen(s);
char *str = reinterpret_cast(malloc(m_length + len + 1));
if (str != nullptr)
{
strncpy(str, m_str, i);
strncpy(str + i, s, len);
strncpy(str + i + len, m_str + i, m_length - i);
str[len + m_length] = '\0';
free(m_str);
m_str = str;
m_length = m_length + len;
}
else
{
THROW_EXCEPTION(NoEnoughMemoryException, "No memory to insert str object ...");
}
}
}
else
{
THROW_EXCEPTION(IndexOutOfBoundsException, "Parameter i is invalid");
}
return *this;
}
String &String::insert(size_t i, const String &s)
{
return insert(i, s.str());
}
String &String::trim()
{
size_t b = 0;
size_t e = m_length - 1;
while (m_str[b] == ' ') b++;
while (m_str[e] == ' ') e--;
if (b == 0)
{
m_str[e + 1] = '\0';
m_length = e + 1;
}
else
{
for (size_t i=0, j = b; j<=e; ++i, ++j)
{
m_str[i] = m_str[j];
}
m_str[e - b + 1] = '\0';
m_length = e - b + 1;
}
return *this;
}
int String::indexOf(const char *s) const
{
return kmp(m_str, s);
}
int String::indexOf(const String &s) const
{
return kmp(m_str, s.m_str);
}
String &String::remove(size_t i, size_t len)
{
if (i < m_length)
{
size_t n = i;
size_t m = i + len;
while ((n < m) && (m < m_length))
{
m_str[n++] = m_str[m++];
}
m_str[n] = '\0';
m_length = n;
}
return *this;
}
String &String::remove(const char *s)
{
return remove(indexOf(s), s ? strlen(s) : 0);
}
String &String::remove(const String &s)
{
return remove(indexOf(s), s.length());
}
String &String::replace(const char *t, const char* s)
{
int index = indexOf(t);
if (index >= 0)
{
remove(t);
insert(index, s);
}
return *this;
}
String &String::replace(const String &t, const char *s)
{
return replace(t.str(), s);
}
String &String::replace(const char *t, const String &s)
{
return replace(t, s.str());
}
String &String::replace(const String &t, const String &s)
{
return replace(t.str(), s.str());
}
String String::sub(size_t i, size_t len) const
{
String ret;
if (i < m_length)
{
if (len + i > m_length) len = m_length - i;
char *str = reinterpret_cast(malloc(len + 1));
if (str != nullptr)
{
strncpy(str, m_str + i, len);
str[len] = '\0';
ret = str;
}
free(str);
}
else
{
THROW_EXCEPTION(IndexOutOfBoundsException, "Parameter i is Invalid ...");
}
return ret;
}
bool String::operator == (const char *s) const
{
return (strcmp(m_str, s ? s : "") == 0);
}
bool String::operator == (const String &s) const
{
return (strcmp(m_str, s.str()) == 0);
}
bool String::operator != (const char *s) const
{
return (strcmp(m_str, s ? s : "") != 0);
}
bool String::operator != (const String &s) const
{
return (strcmp(m_str, s.str()) != 0);
}
bool String::operator > (const char *s) const
{
return (strcmp(m_str, s ? s : "") > 0);
}
bool String::operator > (const String &s) const
{
return (strcmp(m_str, s.str()) > 0);
}
bool String::operator < (const char *s) const
{
return (strcmp(m_str, s ? s : "") < 0);
}
bool String::operator < (const String &s) const
{
return (strcmp(m_str, s.str()) < 0);
}
bool String::operator >= (const char *s) const
{
return (strcmp(m_str, s ? s : "") >= 0);
}
bool String::operator >= (const String &s) const
{
return (strcmp(m_str, s.str()) >= 0);
}
bool String::operator <= (const char *s) const
{
return (strcmp(m_str, s ? s : "") <= 0);
}
bool String::operator <= (const String &s) const
{
return (strcmp(m_str, s.str()) <= 0);
}
String String::operator + (const char *s) const
{
String ret;
size_t len = m_length + strlen(s ? s : "");
char *str = reinterpret_cast(malloc(len + 1));
if (str != nullptr)
{
strcpy(str, m_str);
strcat(str, s ? s : "");
free(ret.m_str);
ret.m_str = str;
ret.m_length = len;
}
else
{
THROW_EXCEPTION(NoEnoughMemoryException, "No memory to create str object ...");
}
return ret;
}
String String::operator + (const String &s) const
{
return (*this + s.str());
}
String &String::operator += (const char *s)
{
return (*this = *this + s);
}
String &String::operator += (const String &s)
{
return (*this = *this + s.str());
}
String String::operator - (const char *s) const
{
return String(*this).remove(s);
}
String String::operator - (const String &s) const
{
return String(*this).remove(s);
}
String &String::operator -= (const char *s)
{
return remove(s);
}
String &String::operator -= (const String &s)
{
return remove(s);
}
String &String::operator = (const char *s)
{
if (m_str != s)
{
char *str = strdup(s ? s : "");
if (str != nullptr)
{
free(m_str);
m_str = str;
m_length = strlen(str);
}
else
{
THROW_EXCEPTION(NoEnoughMemoryException, "No memory to create str object ...");
}
}
return *this;
}
String &String::operator = (const char c)
{
char s[] = {c, '\0'};
return (*this = s);
}
String &String::operator = (const String &s)
{
return (*this = s.str());
}
char &String::operator[] (size_t i)
{
if (i < m_length)
{
return m_str[i];
}
else
{
THROW_EXCEPTION(InvalidParameterExcetion, "Parameter i invalid...");
}
}
char String::operator[] (size_t i) const
{
return const_cast(*this)[i];
}
String::~String()
{
free(m_str);
}
} 文件：main.cpp
#include
#include "DTString.h"
using namespace std;
using namespace DTLib;
int main()
{
String s = "ababax";
cout << s.indexOf("ax") << endl;
cout << s.indexOf("c") << endl;
cout << "-------------" << endl;
cout << s.remove(0, 1).str() << endl;
cout << s.remove("ba").str() << endl;
cout << s.remove(String("x")).str() << endl;
cout << "-------------" << endl;
String s1 = "abcde";
String s2 = s1 - "bcd";
cout << s1.str() << endl;
cout << s2.str() << endl;
cout << "-------------" << endl;
String s3 = "ababax";
cout << s3.replace("ba", "xyz").str() << endl;
cout << "-------------" << endl;
String s4 = "abcde";
String s5 = s4.sub(1, 3);
cout << s4.str() << endl;
cout << s5.str() << endl;
return 0;
} 输出：
4
-1
-------------
babax
bax
ba
-------------
abcde
ae
-------------
axyzbax
-------------
abcde
bcd小结
- 字符串类是工程开发中必不可少的组件
- 字符串中应该包含常用字符串操作函数
- 增：insert, operator +, ...
- 删：remove, operator -, ...
- 查：indexOf, ...
- 改：replace, ...
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