[英]Questions regarding C++ string
phrase.erase(remove_if (phrase.begin(), phrase.end(), ::isdigit), phrase.end());
In the above code, why do I have to use ::
even though I used using namespace std
? 在上面的代码中,即使
using namespace std
,为什么也必须使用::
?
#include "Palindrome.h"
#include <iostream>
#include <string.h>
#include <algorithm>
using namespace std;
Palindrome::Palindrome (string Phrase){
phrase=Phrase;
}
void Palindrome::removeNonLetters()
{
phrase.erase(remove_if (phrase.begin(), phrase.end(), ::isdigit), phrase.end());
phrase.erase(remove_if (phrase.begin(), phrase.end(), ::ispunct), phrase.end());
phrase.erase(remove_if (phrase.begin(), phrase.end(), ::isspace), phrase.end());
}
void Palindrome::lowerCase()
{
for (int i=0; i<phrase.length(); i++)
{
phrase[i] = tolower(phrase[i]);
}
}
bool Palindrome::isPalindrome()
{
int length=phrase.length();
int a=0;
for (int i=0;i<length/2;i++)
{
if(phrase[i] != phrase[length-a-1])
{
return false;
break;
}
a++;
}
return true;
}
The above code is to check if the string is a Palindrome. 上面的代码是检查字符串是否是回文。 I don't understand why I need to use the first part which is
我不明白为什么我需要使用第一部分
Palindrome::Palindrome (string Phrase){
phrase=Phrase;
}
I will always get "yes" if I deleted the above part. 如果我删除了上面的部分,我将总是“是”。
The test code in main is 主要的测试代码是
if(test.Palindrome::isPalindrome() == 1){
cout<<"Yes"<<endl;
}
else {
cout<<"No"<<endl;
}
One more question. 还有一个问题。 I try to change the lowercase of above code, I got error.
我尝试更改上述代码的小写字母,但出现错误。 Do anyone know what happen with it?
有人知道会发生什么吗? The new code was from https://www.geeksforgeeks.org/conversion-whole-string-uppercase-lowercase-using-stl-c/
新代码来自https://www.geeksforgeeks.org/conversion-whole-string-uppercase-lowercase-using-stl-c/
Before 之前
void Palindrome::lowerCase()
{
for (int i=0; i<phrase.length(); i++)
{
phrase[i] = tolower(phrase[i]);
}
}
After 后
void Palindrome::lowerCase(){
transform(phrase.begin(), phrase.end(), phrase.begin, ::tolower);
} }
Can anyone explain it to me? 谁能向我解释? Many thanks!
非常感谢!
There are multiple isdigit
, ispunct
, and isspace
functions - ones in the global namespace in the <ctype.h>
header, and several in the std
namespace in the <cctype>
and <clocale>
headers. 有多个
isdigit
, ispunct
和isspace
函数-在<ctype.h>
头文件的全局命名空间中,在<cctype>
和<clocale>
头文件的std
命名空间中有多个。 Prefixing them with ::
says you want to use the ones from the global namespace. 用
::
前缀表示您要使用全局名称空间中的那些。
You need to use <string>
instead of <string.h>
in order to use the std::string
class. 为了使用
std::string
类,您需要使用<string>
而不是<string.h>
。
Assuming test
is a Palindrome
object, then test.Palindrome::isPalindrome()
should be just test.isPalindrome()
. 假设
test
是Palindrome
对象,则test.Palindrome::isPalindrome()
应该只是test.isPalindrome()
。
If you omit the Palindrome
constructor, then the phrase
member remains blank, and your isPalindrome()
implementation returns true
for a blank phrase
( length
is 0) because there is nothing for the for
loop to check. 如果省略
Palindrome
构造函数,则phrase
成员保持空白,并且isPalindrome()
实现对空白phrase
( length
为0)返回true
,因为for
循环无需检查。 Which is technically correct - a blank string is a palindrome. 从技术上讲这是正确的-空字符串是回文。
The ::
indicates that you're using isdigit
and the others from the global namespace. ::
表示您正在使用isdigit
,而其他人则使用全局命名空间。 The isdigit
is a part of other header files, such as <ctype.h>
. isdigit
是其他头文件的一部分,例如<ctype.h>
。
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