有做适当的问题 [英] Having problem to do appropriately
问题描述
问题
创建一个AlphaString类，该类仅将字母存储在任意长度的字符串中.该字符串具有一个构造函数，可确保该字符串仅包含字母.该类还具有一个复制构造函数和一个重载的+运算符.重载的+运算符应执行两个字符串的串联.
Question
Create a class AlphaString that stores only alphabets in a string of arbitrary length. The string has a constructor that makes sure that String has only Alphabets. The class also has a copy constructor, and an overloaded + operator. The overloaded + operator should perform the concatenation of two strings.
#include <string.h>
#include<iostream.h>
#include<conio.h>
using namespace std;
class AlphaString {
public:
AlphaString( char *ch ); // Declare constructor
~AlphaString(); // and destructor.
private:
char *_text;
size_t sizeOfText;
};
AlphaString::AlphaString( char *ch ) {
int i=1;
int k=int(ch[i]);
int flag=0;
while(strlen(ch))
{
if((k>=65 && k<=90) || (k>=97 && k<=122))
flag =0;
else
{
flag =1;
break;
}
k=int(ch[i]);
i++;
}
sizeOfText = strlen( ch ) + 1;
if(flag==0)
{
// Dynamically allocate the correct amount of memory.
_text = new char[ sizeOfText ];
}
}
// Define the destructor.
AlphaString::~AlphaString() {
// Deallocate the memory that was previously reserved
// for this string.
if (_text)
delete[] _text;
}
// Copy Constructor.
AlphaString::AlphaString(AlphaString & objB) {
}
int main() {
char str[25];
cout<<"Enter First String: ";
cin>>str;
AlphaString ob1(str);
cout<<"Enter Second String: ";
cin>>str;
AlphaString ob2(str);
cout<<ob1._text+ob2._text;
AlphaString ob3(ob1);
getch();
return 0;
}
[edit]添加了代码块以保留格式-OriginalGriff [/edit]
[edit]正确的代码对齐和大括号-Andrew Brock [/edit]
[edit]Code block added to preserve formatting - OriginalGriff[/edit]
[edit]Corrected code alignment and balanced braces - Andrew Brock[/edit]
推荐答案
AlphaString::AlphaString( char *ch ) { //You are not changing the contents of ch, so why not make it const?
int i=1; //All array indices start at 0 in C++. Strings included.
int k=int(ch[i]); //This is the 2nd character in the string
int flag=0; //You should use meaningful variable names, like onlyAlpha
//while(strlen(ch)) is just horrid.
//The length of the string never changes, so you might as well have while(1)
//Furthermore, strlen works by iterating over every character in the string to find the termination character. This is happening every loop.
while(strlen(ch))
{
if((k>=65 && k<=90) || (k>=97 && k<=122)) //Why not use characters (as Richard MacCutchan suggested)
flag =0; //flag is already 0. Why are you setting it again?
else
{
flag =1;
break;
}
k=int(ch[i]);
i++;
}
sizeOfText = strlen( ch ) + 1;
if(flag==0)
{
// Dynamically allocate the correct amount of memory.
_text = new char[ sizeOfText ];
//What are the contents of _text? It is not the string.
}
//What happens to _text if flag != 0?
//It remains uninitialised, and likely does not hold the value NULL.
//This will cause problems with the destructor.
更正的解决方案:
A corrected solution:
AlphaString::AlphaString(const char *ch) : _text(0), sizeOfText(0) {
int i = 0;
bool bOnlyAlpha = true; //You should use meaningful variable names, like onlyAlpha
while(ch[i] != 0) { //0 is the null terminator
if((ch[i]<''A'' || ch[i]>''Z'') && (ch[i]<''a'' || ch[i]>''z''))
flag =0; //flag is already 0. Why are you setting it again?
bOnlyAlpha = false;
break;
}
++i;
}
sizeOfText = i + 1; //If you are paying attention, you will notice that i holds the length of the string, not including the terminator
if (bOnlyAlpha) {
// Dynamically allocate the correct amount of memory.
_text = new char[sizeOfText];
memcpy(_text, ch, sizeOfText); //Could use strcpy, but memcpy is faster
}
}
我想你想要这样的东西:
I think you want something like this:
#include<ctype.h>
class AlphaString
{
public:
AlphaString( char *ch );
// Declare constructor
~AlphaString();
// and destructor.
private:
char *_text;
size_t sizeOfText;
};
AlphaString::AlphaString( char *ch )
: _text(0),sizeOfText(0)
// Initialize to make sure they don''t contain garbage,
// as required by your destructor
{
if(ch)
{
size_t numberOfCharacters = 0;
char* ptr = ch;
while(*ptr) // figure out the required memory size
{
char c = *ptr;
if(isalpha(c))
{
numberOfCharacters++;
}
ptr++;
}
if(numberOfCharacters)
{
_text = new char[numberOfCharacters+1];
char* ptrSource = ch;
char* ptrDestination = _text;
while(*ptrSource) // copy the alphbetic characters
{
char c = *ptrSource;
if(isalpha(c))
{
*ptrDestination = c;
ptrDestination++;
}
ptrSource++;
}
_text[numberOfCharacters] = ''\x0''; // zero terminate the string
sizeOfText = numberOfCharacters;
}
}
}
这应该工作:)-您可以使用自己的析构函数实现...
该构造函数解决了一些重要问题:
1.成员变量的初始化:
_text(0),sizeOfText(0)
C ++不会初始化成员变量，这是您必须自己执行的事情.
2. if(ch)测试ch是否不为NULL –如果是，则原始代码有问题
3.计算字母字符的数量
4.如果有任何字母字符-分配所需的内存量:
字母字符数+ 1(用于终止零)
5.仅将字母字符 复制到分配的缓冲区
6.零终止缓冲区
问候
Espen Harlinn
This should work :) - you can use your own destructor implementation ...
This constructor addresses a few important points:
1. Initialization of member variables:
_text(0),sizeOfText(0)
C++ does not initialize member variables, that’s something you have to perform yourself.
2. if(ch) tests if ch is not NULL – if it is, the original code is in trouble
3. count the number of alphabetic characters
4. if there are any alphabetic characters - allocate the required amount of memory:
number of alphabetic characters + 1 (for terminating zero)
5. copies only the alphabetic characters to the allocated buffer
6. zero terminates the buffer
Regards
Espen Harlinn
if((k>=65 && k<=90) || (k>=97 && k<=122))
为什么不通过以下代码来使其可读:
Why not make it readable by coding like:
if((k >= ''A'' && k <= ''Z'') || (k >= ''a'' && k <= ''z''))
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