C/C++面试常见题目之字符串操作（二）

爱被打了一巴掌 2022-03-16 10:42 134阅读 0赞

字符串是一种常用的数据类型，现在我们将其常用的功能用代码实现如下：

class String
    {
    	char* ptr;
    	int len;
    public:
    /*********************************无参构造*********************************/
    	String() {
    		ptr = new char[1]{'\0'};
    		len = 0;
    	}
    /*********************************拷贝构造*********************************/	
    	String(const char* s) {
    		cout << "const char* "<< endl;
    		len = strlen(s);
    		ptr = new char[len+1];
    		memcpy(ptr, s, len+1);
    	}
    	/*********************************拷贝构造*********************************/
    	String(char c, int n) {
    		len = n;
    		ptr = new char[n+1]{};
    		memset(ptr, c, n);
    	}
    	//const String& 拷贝构造函数的原型, 
    	//1，引用可以改变实参，不应该改变实参的内容
    	//2，const & 可以引用右值(匿名变量)
    	/*********************************拷贝构造*********************************/
    	String(const String& s) {
    		cout << "copy " << endl;
    		len = s.len;
    		ptr = new char[s.len+1]{};
    		memcpy(ptr, s.ptr, len);
    	}
    	/*********************************字符串长度*********************************/
    	int size() {
    		return len;
    	}
    	/*********************************判断字符串是否为空*********************************/
    	bool empty() {
    		return len == 0;
    	}
    	/*********************************字符串首地址*********************************/
    	const char* c_str() {
    		return ptr;
    	}
    	/*********************************字符串长度重置*********************************/
    	void resize(int n) {
    		char* p = new char[n+1]{};
    		memcpy(p, ptr, n);
    		delete [] ptr;
    		ptr = p;
    		len = n;
    	}
    	// ptr = "hello" 
    	//        hlo  
    	//	p  = "000"
    	//				1,  2
    	/*********************************字符串删除*********************************/
    	void erase(int pos, int n) {
    		if (pos < 0 || pos >= len) {
    			cout << "超出范围" << endl;
    			abort();
    		} 
    		if (n < 0) {
    			cout << "长度小于0" << endl;
    			abort();
    		}
    		n = n > len - pos ? len - pos : n;
    		
    		char* p = new char[len-n+1]{};
    		memcpy(p, ptr, pos);
    		memcpy(p+pos, ptr+pos+n, len-pos-n);
    		delete [] ptr;
    		ptr = p;
    		len = len - n;
    	}
    	/*********************************字符串头插入*********************************/
    	void insert(int pos, const char* s) {
    		replace(pos, 0, s);
    	}						
    					//	"he\0llo"
    	/*********************************字符串任意插入*********************************/
    	void insert(int pos, const String& s) {
    		replace(pos, 0, s);
    	}
    	/*
    			  pos+n
    	           | |
    	// ptr = "hello",  s = "world"
    			   --
    	//               1,     2
    	// ptr = "hworldlo";
    			   -----
    */
    /*********************************字符串任意插入*********************************/
    	void replace(int pos, int n, const String& s) {
    		if (pos < 0 || pos >= len) {
    			cout << "超出范围" << endl;
    			abort();
    		} 
    		if (n < 0) {
    			cout << "长度小于0" << endl;
    			abort();
    		}
    		n = n > len - pos ? len - pos : n;
    		int sl = s.len; //String类型的长度不能用strlen测量
    		char* p = new char[len+sl-n+1]{};
    		memcpy(p, ptr, pos);
    		memcpy(p+pos, s.ptr, sl);
    		memcpy(p+pos+sl, ptr+pos+n, len-pos-n);
    		len = sl + len - n;
    		delete [] ptr;
    		ptr = p;
    	}
    	/*********************************字符串任意替换*********************************/
    	void replace(int pos, int n, const char* s) {
    		if (pos < 0 || pos >= len) {
    			cout << "超出范围" << endl;
    			abort();
    		} 
    		if (n < 0) {
    			cout << "长度小于0" << endl;
    			abort();
    		}
    		n = n > len - pos ? len - pos : n;
    		int sl = strlen(s);
    		char* p = new char[len+sl-n+1]{};
    		memcpy(p, ptr, pos);
    		memcpy(p+pos, s, sl);
    		memcpy(p+pos+sl, ptr+pos+n, len-pos-n);
    		len = sl + len - n;
    		delete [] ptr;
    		ptr = p;
    	}
    	/*********************************字符串查找*********************************/
    	String substr(int pos, int n) {
    		//	ptr[pos] ~ ptr[pos+n-1]
    		if (pos < 0 || pos >= len) {
    			cout << "超出范围" << endl;
    			abort();
    		} 
    		if (n < 0) {
    			cout << "长度小于0" << endl;
    			abort();
    		}
    		n = n > len - pos ? len - pos : n;
    		char* p = new char[n+1];
    		memcpy(p, ptr+pos, n);
    		String t;
    		delete [] t.ptr;
    		t.ptr = p;
    		t.len = n;
    		return t;
    	}
    	void show() {
    		cout << (void*)ptr << " ";
    		for (int i=0; i<len; i++)
    			cout << ptr[i];
    		cout << endl;
    	}
    	String show(String s) {
    		s.show();
    		String t("banana");
    		return t;
    	}
    	//析构函数
    	~String() {
    		cout << "delete " << ptr <<endl;
    		delete [] ptr;
    	}
    };