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//header.h

#ifndef _HEADER_H

#define _HEADER_H

#define defaultSize 128

#include<iostream>

#include<string.h>

using namespace std;

class myString

{

    private:

        char *ch;

        int curLength;

        int maxSize;

    public:

        myString(int sz=defaultSize);

        myString(const char *init);

        myString(const myString& ob);

        ~myString(){delete []ch;}

        void print();

        int Length()const;

        myString operator()(int pos, int len);

        myString& operator = (myString& ob);

};

myString& myString::operator = (myString& ob)

{

    if(&ob!=this)

    {

        delete[]ch;

        this->ch = new char[ob.maxSize];

        this->maxSize = ob.curLength;

        strcpy(this->ch, ob.ch);

        this->curLength = ob.curLength;

    }

    else

    {

        cerr<<"String copy error\n";

    }

    return *this;

}

myString myString::operator()(int pos, int len)

{

    myString temp;

    if(pos<0 || len<=0 || pos+len-1>=this->maxSize)

    {

        temp.curLength = 0;

        temp.ch[0] = '\0';

    }

    else

    {

        if(pos+len-1 >= this->curLength)

            len = this->curLength-pos;

        temp.curLength = len;

        for(int i=0,j=pos; i<len; ++i,++j)

            temp.ch[i] = this->ch[j];

        temp.ch[len] = '\0';

    }

    return temp;

}

int myString::Length()const

{

    return this->curLength;

}

void myString::print()

{

    cout<<this->ch<<endl;

}

myString::myString(int sz)

{

    this->maxSize = sz;

    this->ch = new char[this->maxSize+1];

    if(this->ch == NULL)

    {

        cerr<<"Allocation ERROR\n";

        exit(1);

    }

    this->curLength = 0;

    ch[0] = '\0';

}

myString::myString(const char *init)

{

    int len = strlen(init);

    this->maxSize = (len > defaultSize) ? len : defaultSize;

    this->ch = new char[this->maxSize+1];

    if(this->ch == NULL)

    {

        cerr<<"Application Memory ERROR\n";

        exit(1);

    }

    this->curLength = len;

    strcpy(this->ch, init);

}

myString::myString(const myString& ob)

{

    this->maxSize = ob.maxSize;

    this->ch = new char[this->maxSize+1];

    if(this->ch == NULL)

    {

        cerr<<"Application Memory ERROR\n";

        exit(1);

    }

    this->curLength = ob.curLength;

    strcpy(this->ch, ob.ch);

}

#endif

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//main.cpp

#include"header.h"

int main()

{

    myString st(10), st1("ABCDEFG");

    myString st2(st1);

    st.print(), st1.print(), st2.print();

    st = st1(0, 4);//???

    st.print();

    return 0;

}

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int i=0;

++++i;//这样是可以的

i++++;//这样就是错误的