Code analysis of c++ string class
- 2020-06-03 07:47:08
- OfStack
1: review
(1) The string in c++ is often tested in interviews and written tests; Free download of engineering code string class implementation
(2) string class and fstream class in c++ are sharp tools for processing external data.
(3) string class often USES find find_first_of ES18en_ES19en_ES20en_ES24en find_last_of find_ES26en_ES28en substr replace, etc., as well as combined use to reach split and trim in java
(4) The use of friend is only a non-internal declaration in the class but can access the external functions of internal members, and the friend keyword is no longer needed externally; It differs from member functions in that friend and external functions do not contain Pointers to this objects; This article USES the global Max min variable defined by const (instead of #define)
(5) Some functions return MyString & , Char & MyString, Char, etc. This depends on whether the object you return is a local or global variable of the function (or a member of the class's current object); The former can only return 1 MyString, Char, etc. The latter strongly recommends a return to MyString & , Char & Etc. (quote);
(6) Some functions take arguments of const MyString & Some are MyString & (quote); Why is that? The former is to pass the external value inside the subfunction, and is not allowed to change; The latter is passed in as the return value of the function, which is the processing result of the function (rather than the return value of the function itself).
2: The following is a simple implementation of the string class, reference is STL source code, but their understanding is not deep enough, there are inevitably 1 error, please advise
(1) MyString. h file
#ifndef MYSTRING_H
#define MYSTRING_H
#include "MyExcept.h"
#include <cstring>
#include <iostream>
const int INI_MAX = 0x7fffffff;//2^32npos
const int INI_MIN = 0x80000000;// -2^32
const int npos = 0xffffffff;// npos
using namespace std;
class MyString
{
public:
// constructor
MyString();//
MyString(const MyString &);//
MyString(const char *);
MyString(const size_t,const char);
// destructor
~MyString();
// attributes
size_t length();// String length
bool isEmpty();// Returns whether the string is empty
const char* c_str();// return c In the style of trr A pointer to the
// friend funs
// read writer operations
friend ostream& operator<< (ostream&, const MyString&);
friend istream& operator>> (istream&, MyString&);
//add operation
friend MyString operator+(const MyString&,const MyString&);
// compare operations
friend bool operator==(const MyString&,const MyString&);
friend bool operator!=(const MyString&,const MyString&);
friend bool operator<(const MyString&,const MyString&);
friend bool operator<=(const MyString&,const MyString&);
friend bool operator>(const MyString&,const MyString&);
friend bool operator>=(const MyString&,const MyString&);
// Member functions implement operator overloading , Actually, 1 Member function operator overloading is good if you need to return an object of your own 1 some
// index operation
char& operator[](const size_t);
const char& operator[](const size_t)const;
// =
MyString& operator=(const MyString&);
// +=
MyString& operator+=(const MyString&);
// +=
//MyString operator+=(const MyString&); cannot be overloaded
// Member manipulation function
// substr
MyString substr(size_t pos,const size_t n);
// append
MyString& append(const MyString&);
//insert
MyString& insert(size_t,const MyString&);
//assign replace
MyString& assign(MyString&,size_t,size_t);
// erase delete
MyString& erase(size_t,size_t);
//find_first_of To find a 1 A character size_t Nonsign number , overloading
// Finds the first in a string 1 with str Returns the position of a matched character in.
// Search from index Go ahead and return if you don't find it string::npos
int find_first_of(const char* str,size_t index=0);
int find_first_of(const char ch,size_t index=0);
int find_first_of(const MyString &,size_t index=0);
// Look for the value in the string 1 with str Returns the position of a character if none of the characters in. Search from index Start. Return if not found string::nops
int find_first_not_of(const char* str,size_t index=0);
int find_first_not_of(const char ch,size_t index=0);
int find_first_not_of(const MyString&,size_t index=0);
// swap
void swap(MyString& lhs,MyString& rhs);
// replace_all
MyString& replace_all(const char oldc,const char newc=NULL);
MyString& replace(size_t index,size_t num1,size_t num2,const char ch);
//find
int find(const char* str,size_t index=0);
int find(const MyString& str,size_t index=0);
int find(const char ch,size_t index=0);
//private
private:
char *p_str;
size_t strLength;
};
#endif // MYSTRING_H(2) MyString. cpp
#include "MyString.h"
#include <cassert>
// constructor
MyString::MyString():p_str(NULL),strLength(0){}
MyString::MyString(const MyString &str)//
{
if(NULL == str.p_str)
{
return;
}
strLength = str.strLength;
p_str = new char[strLength+1];
strcpy(p_str,str.p_str);
}
MyString::MyString(const char *str)
{
if(NULL == str)
{
return;
}
strLength = strlen(str);
p_str = new char[strLength+1];
strcpy(p_str,str);
}
MyString::MyString(const size_t len,const char ch)
{
if(NULL == ch)
{
return;
}
strLength = len;
p_str = new char[strLength+1];
for(size_t i=0;i<strLength;i++)
{
p_str[i] = ch;
}
p_str[strLength] = '\0';// because strset In order to '\0' The end of the
cout << p_str << " &&" << endl;
//strset(p_str,ch);
//cout << p_str[0] << ",,,"<<strlen(p_str) << "," << strLength << endl;
}
// destructor
MyString::~MyString()
{
delete[] p_str;
}
// attributes
size_t MyString::length()// String length
{
return strLength;
}
bool MyString::isEmpty()// Returns whether the string is empty
{
return strLength==0?true:false;
}
const char* MyString::c_str()
{
return p_str;
}
// Why not quote?? friend Use in the class declaration, the outside is not needed, and the friend function is not a member of the class function, so not MyString : :
// ostream
ostream& operator<< (ostream& out,const MyString &str)
{
if(str.p_str != NULL)
{
out << str.p_str;
}
return out;
}
// istream,1 One is const On the other 1 No, according to the change or the same
istream& operator>> (istream& in, MyString& str)
{
char tmp[100];// Temporary string
if(in>>tmp)
{
delete[] str.p_str;
str.strLength = strlen(tmp);
str.p_str = new char[str.strLength+1];
strcpy(str.p_str,tmp);
}
return in;
}
// + add
MyString operator+(const MyString& lhs,const MyString& rhs)
{
MyString ret;
ret.strLength = lhs.strLength + rhs.strLength;
ret.p_str = new char[ret.strLength+1];
strcpy(ret.p_str,lhs.p_str);
strcat(ret.p_str,rhs.p_str);
return ret;
}
// compare operations
bool operator==(const MyString& lhs,const MyString& rhs)
{
return strcmp(lhs.p_str,rhs.p_str)==0?true:false;
}
bool operator!=(const MyString& lhs,const MyString& rhs)
{
return strcmp(lhs.p_str,rhs.p_str)!=0?true:false;
}
bool operator<(const MyString& lhs,const MyString& rhs)
{
return strcmp(lhs.p_str,rhs.p_str)<0?true:false;
}
bool operator<=(const MyString& lhs,const MyString& rhs)
{
return strcmp(lhs.p_str,rhs.p_str)<=0?true:false;
}
bool operator>(const MyString& lhs,const MyString& rhs)
{
return strcmp(lhs.p_str,rhs.p_str)>0?true:false;
}
bool operator>=(const MyString& lhs,const MyString& rhs)
{
return strcmp(lhs.p_str,rhs.p_str)>=0?true:false;
}
// Member functions implement operator overloading
// index operation
char& MyString::operator[](const size_t index)
{
if(index<0 || index>=strLength)
{
throw Outofbond() ;
}
return p_str[index];
}
const char& MyString::operator[](const size_t index)const
{
if(index<0 || index>=strLength)
{
throw Outofbond();
}
return p_str[index];
}
// = Assignment constructor (determines if it is itself) Why did you delete it this way?
MyString& MyString::operator=(const MyString& other)
{
if(this != &other)
{
if(strLength<other.strLength)
{
delete[] p_str;
p_str = new char[other.strLength+1];
}
strLength = other.strLength;
strcpy(p_str,other.p_str);
}// This may create excess unreleased space
return *this;
}
// += Equivalent to the return of a backup, internal object destruction, does not affect and Not at all 1 The sample of
// MyString MyString::operator+=(const MyString& other)
// {
// if(NULL == other.p_str)
// {
// return *this;
// }
// MyString ret;
// ret.strLength = strLength + other.strLength;
// ret.p_str = new char[ret.strLength+1];
// strcpy(ret.p_str,p_str);
// strcat(ret.p_str,other.p_str);
// return ret;
// }
// Returns a reference to the current object, which is in the calling function and will not be destroyed
// judge 1 Is it the sum of itself
MyString& MyString::operator+=(const MyString& other)
{
if(NULL == other.p_str)
{
return *this;
}
if(this == &other)
{
MyString copy(*this);
return *this += copy;
}// You have to decide whether it's equal, and you have to += Of, that's the same thing as calling itself, but this time I'm going to go straight down and not go in if the
strLength += other.strLength;
//strLength *= 2;
char *p_old = p_str;
p_str = new char[strLength+1];
strcpy(p_str,p_old);
strcat(p_str,other.p_str);
delete[] p_old;// Delete the old space
return *this;
}
// Member manipulation function
// substr Return application is not ok, wrong; Pick up from pos The start of the n A substring of two characters
//MyString& MyString::substr(size_t pos,const size_t n)
MyString MyString::substr(size_t pos,const size_t n)
{
if((pos+n)>=strLength)
{
throw Outofbond();
}
MyString ret;
ret.strLength = n;
//ret.p_str = new char[n+1];
ret.p_str = new char[ret.strLength+1]; // Can also be
for(size_t i=0;i<n;i++)
{
ret.p_str[i] = p_str[pos+i];
}
ret.p_str[n] = '\0';
// for(size_t i=0;i<ret.strLength;i++)
// {
// ret[i] = (*this)[pos+i];
// cout << ret[i] << ",,";
// }// Ok, use the [] that I just reloaded , It's better that way, you don't have to cross the line again , I don't know why, the wrong one
// ret[ret.strLength] = '\0';
return ret;
}
// append with += Append to
MyString& MyString::append(const MyString& other)
{
*this += other;// Take advantage of that heavy load +=
return *this;
}
//insert from pos Initial insertion other
MyString& MyString::insert(size_t pos,const MyString& other)
{
if(pos<0 || pos>=strLength)
{
throw Outofbond();
}
char *p_old = p_str;
strLength += other.strLength;
p_str = new char[strLength+1];
for(size_t i=0;i<pos;i++)
{
*(p_str+i) = *(p_old+i);
}
for(size_t i=pos;i<other.strLength+pos;i++)
{
*(p_str+i) = other.p_str[i-pos];
}
for(size_t i=other.strLength+pos;i<strLength;i++)
{
*(p_str+i) = p_old[i-other.strLength];
}
*(p_str+strLength) = '\0';
return *this;
}
//assign replace with other the POS The start of the n Corresponding to replace this the pos The start of the
MyString& MyString::assign(MyString&other,size_t pos,size_t n)
{
// if(pos<0 || pos>=strLength)
// {
// throw Outofbond();
// }
assert(pos>0 && pos<strLength);// assert The benefits of
assert(pos+n<other.strLength);
if(strLength < pos + n)
{
char *p_old = p_str;
strLength = pos + n;
p_str = new char[strLength+1];
for(size_t i=0;i<pos;i++)
{
*(p_str+i) = *(p_old+i);
}
delete[] p_old;
}
for(size_t i=pos;i<pos+n;i++)
{
*(p_str+i) = other.p_str[i];
}
*(p_str+pos+n) = '\0';
return *this;
}
// erase delete This method is not very good, there is no release erase The space of , Look at the following
// MyString& MyString::erase(size_t pos,size_t n)
// {
// if((pos+n)>strLength)
// {
// throw Outofbond();
// }
// size_t index = pos + n;
// while(*(p_str+index)!='\0')
// {
// *(p_str+index-n) = *(p_str+index);
// ++index;
// }
// *(p_str+index-n) = '\0';
// return *this;
// }
// erase delete from pos The start of the n A character
MyString& MyString::erase(size_t pos,size_t n)
{
if((pos+n)>strLength)
{
throw Outofbond();
}
char *p_old = p_str;
strLength -= n;
p_str = new char[strLength+1];
for(size_t i=0;i<pos;i++)
{
p_str[i] = p_old[i];
}
for(size_t i=pos;i<strLength;i++)
{
p_str[i] = p_old[i+n];
}
*(p_str+strLength) = '\0';
return *this;
}
//find_first_of To find a 1 A character size_t Nonsign number
// Finds the first in a string 1 with str Returns the position of a matched character in.
// Search from index Go ahead and return if you don't find it string::npos
int MyString::find_first_of(const char* str,size_t index)
{
if(NULL == str || index >=strLength)
return npos;
int tmp_len = strlen(str),j;
size_t flag,min_index = INI_MAX;
for(j=0;j<tmp_len;j++)
{
flag = npos;
for(size_t i=index;i<strLength;i++)
{
if(str[j] == p_str[i])
{
flag = i;
break;
}
}
// indexs[j] = flag;
if(flag != npos)
{
min_index = min_index<flag?min_index:flag;
}
}
// for(j=0;j<tmp_len;j++)
// {
// if(indexs[j]!=npos)
// min = min<indexs[j]?min:indexs[j];
// }
if(min_index == INI_MAX)
{
return npos;
// min_index = npos;
// cout << "---npos----" << min_index << ",,,,";
}
return min_index;
}
int MyString::find_first_of(const char ch,size_t index)
{
if(NULL == ch || index >=strLength)
return npos;
int j;
size_t flag = npos;
for(size_t i=index;i<strLength;i++)
{
if(ch == p_str[i])
{
flag = i;
break;
}
}
return flag;
}
int MyString::find_first_of(const MyString& str,size_t index)
{
if(NULL == str || index >=strLength)
return npos;
int j;
size_t flag,min_index = INI_MAX;
for(j=0;j<str.strLength;j++)
{
flag = npos;
for(size_t i=index;i<strLength;i++)
{
if(str[j] == p_str[i])
{
flag = i;
break;
}
}
if(flag != npos)
{
min_index = min_index<flag?min_index:flag;
}
}
if(min_index == INI_MAX)
{
return npos;
}
return min_index;
}
// Look for the value in the string 1 with str Returns the position of a character if none of the characters in.
// Search from index Start. Return if not found string::nops O(N^2)
int MyString::find_first_not_of(const char *str,size_t index)
{
if(NULL == str || index >=strLength)
return npos;
size_t i=0,j=0;
size_t tmp_len = strlen(str);
for(i=index;i<strLength;i++)
{
for(;j<tmp_len;j++)
{
if(p_str[i]==str[j])
break;
}
if(j==tmp_len)
break;// According to the jump out of the inner layer for The condition of the judgment, find is the end of the loop
}
if(i==strLength)
return npos;// Not found, // According to the jump out of the inner layer for The condition of the judgment, find is the end of the loop
return i;
}
int MyString::find_first_not_of(const MyString& str,size_t index)
{
if(NULL == str || index >=strLength)
return npos;
size_t i=0,j=0;
for(i=index;i<strLength;i++)
{
for(;j<str.strLength;j++)
{
if(p_str[i]==str[j])
break;// If equal This round of i It doesn't work. Go ahead 1 wheel
}
if(j==str.strLength)
break;// According to the jump out of the inner layer for The condition of the judgment, find is the end of the loop
}
if(i==strLength)
return npos;// Not found, // According to the jump out of the inner layer for The condition of the judgment, find is the end of the loop
return i;
}
int MyString::find_first_not_of(const char ch,size_t index)
{
if(NULL == ch || index >=strLength)
return npos;
size_t i=0;
for(i=index;i<strLength;i++)
{
if(p_str[i]!=ch)// Slightly different from above. Look 1 I don't have to pay
break;
}
if(i==strLength)
return npos;// Not found, // According to the jump out of the inner layer for The condition of the judgment, find is the end of the loop
return i;
}
// swap They have to become, so no const
void MyString::swap(MyString& lhs,MyString& rhs)
{
lhs.strLength ^= rhs.strLength;
rhs.strLength ^= lhs.strLength;
lhs.strLength ^= rhs.strLength;
char *p_tmp = rhs.p_str;
rhs.p_str = lhs.p_str;
lhs.p_str = p_tmp;
}
// replace_all It's still not easy to get. It's not ideal
MyString& MyString::replace_all(const char oldc,const char newc)
{
if(NULL == oldc)
{
return *(this);
}
for(size_t i=0;i<strLength;i++)
{
if(p_str[i] == oldc)
{
p_str[i] = newc;
}
}
return *(this);
}
MyString& MyString::replace(size_t index,size_t num1,size_t num2,const char ch)
{
}
// find function
int MyString::find(const char* str,size_t index)
{
assert(str!=NULL&&index<strLength);
// kmp In the getnext function
size_t len = strlen(str);
size_t next[len+1];
size_t j,k;
next[0] = npos;
j = 0;
k = npos;
while(j<len)
{
if(k==npos || str[j]==str[k])
{
j++;
k++;
next[j] = k;
}
else
k = next[k];
}
// kmp algorithm
k = index;
j = 0;
while(p_str[k]!='\0')
{
if(j==0 || p_str[k]==str[j])
{
k++;
j++;
}
else
{
j = next[j];// Eliminate pointer backtracking
}
if(str[j] == '\0')// The match is successful
return k-j;
}
return npos;
}
int MyString::find(const MyString& str,size_t index)
{
// if(this == &str)
// {
// MyString other(*this);
// find(other,index);
// }
assert(NULL!=str && index<strLength);
// kmp In the getnext function
size_t next[str.strLength+2];
size_t j,k;
next[0] = npos;
j = 0;
k = npos;
while(j<str.strLength)
{
if(k==npos || str.p_str[j]==str.p_str[k])
{
j++;
k++;
next[j] = k;
}
else
k = next[k];
}
int i;
for(i=1;i<=j;i++)
cout << next[i] << ",";
// kmp algorithm
k = index;
j = 0;
while(p_str[k]!='\0')
{
if(j==0 || p_str[k]==str.p_str[j])
{
k++;
j++;
}
else
{
j = next[j];// Eliminate pointer backtracking
}
if(str.p_str[j] == '\0')// The match is successful , I don't know why I'm calling myself str[] Overloading always gives an error
return k-j;
}
if(str.p_str[j] == '\0')// with 1 A string
return k-j;
return npos;
}
int MyString::find(const char ch,size_t index)
{
assert(NULL!=ch && index<strLength);
for(size_t i=index;i<strLength;i++)
{
if(p_str[i] == ch)
return i;
}
return npos;
}
(3) Test function main. cpp
#include "MyString.h"
#include <iostream>
using namespace std;
int main()
{
int n;
int choose = 1;
int p,l;
char cs[100];
MyString s1;
MyString s2("hello");
MyString s3 = "HELLO";
cout << "***** welcome *****\n";
cout << "******* MADE BY zyp **********\n";
cout << "s1= " << s1 << "s2= " << s2 << "s3= " << s3 << endl;
cout << " Please enter the 1 Length less than 100 String of: for example world\n";
cin >> s1;
s1 = s1;
//s1 = s1+s1;
s1 += s1;
MyString s4(s1);
s4.append(s1);
s2.insert(2,s3);
s1.erase(4,4);
s1.assign(s2,1,7);
cout << "s1= " << s1 << "s2= " << s2 << "s3= " << s3 << "s4= " << s4 << endl;
s2 = s4.substr(2,7);
cout << "s4[3]= " << s4[3] << s4.length() << (s1>=s2) << "s4.substr() " << s2 << endl;
cout << "s1.find_first_of(beLE,2) : " << s1.find_first_of("beLE",2) << ",s1.find_first_of(a,3):" << s1.find_first_of('a',3) << ",s1.find_first_of(s3,2):" << s1.find_first_of(s3,2) << endl;
MyString s5(5,'b');
s5 += s5;
//s5.append(s5);// I don't know why I can't append
cout << "s5 = " << s5 << "s5.find_first_not_of(aeHLEOl,2) : " << s5.find_first_not_of("aeHLEOl",2) << "s5.find_first_not_of(aeHLEOl,0) : " << s5.find_first_not_of("aeHLEOl") << endl;
cout << "s5.find_first_not_of(s1,2) : " << s5.find_first_not_of(s1,2) << "s5.find_first_not_of(b,2) : " << s5.find_first_not_of('b',2) << endl;
swap(s1,s5);
s5.replace_all('a','J');
MyString s6("LLO");
cout << s1 << "," << s5 << "s5.find(LLO,0) " << s5.find("LLO",0) << "s5.find(s6,0) " << s5.find(s5) << endl;
cout << npos << endl;
return 0;
}
3: comprehension
(1) It took nearly 2 days to realize it. Rather than learn a lot from it, it is better to know string class again.
(2) I know this simple string class, string source code is far far away; But it has helped me to understand the string class better, or at least to use it more easily.
(3) simple realization of 1 string class, reference is STL source code, but their understanding is not deep enough, there are inevitably 1 error, please advise, thank you very much!
(4) Next step: Enter list