C++中的空字符常量
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Empty character constant in c++
提问by BeepBoop
I copied this code from a tutorial to play around with, however I kept on getting an error that stated that I can't have any empty character constants. the tutorial was in VS 2008, and I am using VS 2013, so perhaps this is no longer valid, but I can't find any fix. here is the code:
我从教程中复制了这段代码来玩，但是我一直收到一个错误，指出我不能有任何空字符常量。该教程是在 VS 2008 中使用的，我使用的是 VS 2013，所以这可能不再有效，但我找不到任何修复方法。这是代码：
#include "stdafx.h"
#include <iostream>
class MyString
{
private:
char *m_pchString;
int m_nLength;
public:
MyString(const char *pchString="")
{
// Find the length of the string
// Plus one character for a terminator
m_nLength = strlen(pchString) + 1;
// Allocate a buffer equal to this length
m_pchString = new char[m_nLength];
// Copy the parameter into our internal buffer
strncpy(m_pchString, pchString, m_nLength);
// Make sure the string is terminated
//this is where the error occurs
m_pchString[m_nLength-1] = '';
}
~MyString() // destructor
{
// We need to deallocate our buffer
delete[] m_pchString;
// Set m_pchString to null just in case
m_pchString = 0;
}
char* GetString() { return m_pchString; }
int GetLength() { return m_nLength; }
};
int main()
{
MyString cMyName("Alex");
std::cout << "My name is: " << cMyName.GetString() << std::endl;
return 0;
}
The error I get is the following:
我得到的错误如下：
Error 1 error C2137: empty character constant
Any help will be greatly appreciated
任何帮助将不胜感激
Thanks again.
再次感谢。
回答by Tommy Andersen
This line:
这一行：
m_pchString[m_nLength-1] = '';
What you probably mean is:
你的意思大概是：
m_pchString[m_nLength-1] = 'm_pchString[m_nLength-1] = 0;
';
Or even:
甚至：
##代码##Strings are zero terminated, which is written as a plain 0or the null character '\0'. For double quote strings ""the zero termintation character is implicitly added to the end, but since you explicitly set a single character you must specify which.
字符串以零结尾，写为普通0字符或空字符'\0'。对于双引号字符串""，零终止字符被隐式添加到末尾，但由于您显式设置了单个字符，因此您必须指定哪个字符。
回答by AnatolyS
what do you think about null-terminated string? Yes, you are right, such strings must be terminated with null:
您如何看待以空字符结尾的字符串？是的，你是对的，这样的字符串必须以 null 结尾：
m_pchString[m_nLength-1] = 0;
m_pchString[m_nLength-1] = 0;
回答by scohe001
You've said that you "get an error stating that strncpy is unsafe to use if i use the null terminator,"but you use strlen, which simply does not workif the string isn't null terminated. From cplusplus:
你说过你“得到一个错误，指出如果我使用空终止符，使用 strncpy 是不安全的”，但是你使用strlen，如果字符串不是空终止，它根本不起作用。从cplusplus：
The length of a C string is determined by the terminating null-character
C 字符串的长度由终止空字符决定
My suggestion to you would be to use null or 0 like others are suggesting and then just use strcpyinstead of strncpyas you copy the whole string every time anyways.
我对您的建议是像其他人建议的那样使用 null 或 0，然后每次都使用strcpy而不是strncpy复制整个字符串。
