声明与 "AString &AString::operator=(AString &ob)" 不兼容

#ifndef ASTRING_H
#define ASTRING_H
#define defaultSize 128//////字符串的最大长度
#include<iostream>
using namespace std;
class AString {
	char* ch;
	int curLength;
	int maxSize;
public:
	AString(int sz = defaultSize);
	AString(const char* init);
	AString(const AString& ob);
	~AString() { delete[]ch; };
	int Length()const { return curLength; }
	AString& operator()(int pos, int len);
	bool operator == (AString&ob)const
	{
		return strcmp(ch, ob.ch) == 0;
	}
	bool operator!=(AString&ob)const
	{
		return strcmp(ch, ob.ch) != 0;
	}
	bool operator!()const
	{
		return curLength == 0;
	}
	AString& operator=(AString& ob);
	AString& operator+=(AString& ob);
	char& operator[](int i);
	int Find(AString& pat, int k)const;
};
AString::AString(int sz)
{
	maxSize = sz;
	ch = new char[maxSize + 1];
	if (ch == NULL)
	{
		cerr << "存储分配错！\n"; exit(1);
	}
	curLength = 0;
	ch[0] = '\0';
};
AString::AString(const char* init)
{
	int len = strlen(init);
	maxSize = (len > defaultSize) ? len : defaultSize;
	ch = new char[maxSize + 1];
	if (ch == NULL)
	{
		cerr << "存储分配出错！\n"; exit(1);
	}
	curLength = len;
	strcpy_s(ch, sizeof(init) + 1, init);
};
AString::AString(const AString& ob)
{
	maxSize = ob.maxSize;
	ch = new char[maxSize + 1];
	if (ch == NULL)
	{
		cerr << "存储分配出错！\n"; exit(1);
	}
	curLength = ob.curLength;
	strcpy_s(ch, sizeof(ob.ch) + 1, ob.ch);
};
AString& AString::operator=(const AString& ob)
{
	if (&ob != this)
	{
		delete[]ch;
		maxSize = ob.maxSize;
		ch = new char[ob.maxSize + 1];
		if (ch == NULL)
		{
			cerr << "存储分配失败！\n"; exit(1);
		}
		curLength = ob.curLength;
		strcpy_s(ch, sizeof(ob.ch) + 1, ob.ch);
	}
	else
		cout << "字符串自身赋值出错！\n";
	return *this;
};

#endif

AString& operator=(AString& ob);

AString& AString::operator=(const AString& ob)

你这个=重载申明和函数体的定义写的不一样，函数体定义中参数多了const。把const去掉即可

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