将两个const char *组合在一起 [英] Combining two const char* together

问题描述

我尝试了很多方法来做到这一点，我得到了一个静态的，是在控制台类，我做的一个void，它自己工作很好：

  Console :: WriteLine（const char * msg）
  

我得到了另一个const char *非静态void调用控制台:: WriteLine void从它，我一直在C＃上工作了大约一年，在C＃我可以轻松地做这样的：

  string a =Start; 
 string b = a +End; 
  

当我在C ++上调用这个时，它给我一堆错误：

  Player :: Kill（const char * Message）
 {
 Console :: WriteLine（>+ Message + ;）; 
} 
  

我也试过了strcat的东西，使用strcat_s这不是真的工作，我也试图做字符串而不是const char *，并尝试char *，但所有的人给我的错误我想做的事情。

解决方案

const表示无法更改（* 1）。所以你不能简单地添加一个const char字符串到另一个（* 2）。你可以做的是将它们复制到非const字符缓冲区。

  const char * a = ...; 
 const char * b = ...; 
 
 char buffer [256]; //<  -  danger，只存储256个字符。 
 strncpy（buffer，a，sizeof（buffer））; 
 strncat（buffer，b，sizeof（buffer））; 
 
 //现在缓冲区有两个字符串连接在一起。 
  

您尝试使用std :: string失败的原因相似。您说：

  std :: string a =Start; 
 std :: string b = a +End; 
  

这转换为

  b =（std :: string）a +（const char *）End; 
  

除非创建一个额外的字符串，否则应该确定

  std :: string a =Start; 
 a + =End; 
  

如果你正在编译错误，请张贴他们（确保#include）。 / p>

或者你可以这样做：

  std :: string addTwoStrings （const std :: string& a，const std :: string& b）
 {
 return a + b; //因为它们都是字符串。 
} 
  

所有以下工作：（see live demo http://ideone.com/Ytohgs ）

  #include< iostream> 
 #include< string> 
 
 std :: string addTwoStrings（const std :: string& a，const std :: string& b）
 {
 return a + b; //因为它们都是字符串。 
} 
 
 void foo（const char * a，const char * b）
 {
 std :: string str = a; 
 std :: cout<< 1st str = [<< str<< ]<< std :: endl; 
 str + =; 
 std :: cout<< 2nd str = [<< str<< ]<< std :: endl; 
 str + = b; 
 std :: cout<< 3rd str = [<< str<< ]<< std :: endl; 
 str = addTwoStrings（a，）; 
 std :: cout<< 4th str = [<< str<< ]<< std :: endl; 
 str = addTwoStrings（str，b）; 
 std :: cout<< 5th str = [<< str<< ]<< std :: endl; 
} 
 
 int main（）
 {
 foo（hello，world）; 
} 
  

* 1或更准确地说，不能原位更改可以在表达式等中使用它，例如

  const size_t len = strlen（hello）; 
 size_t newLen = len + strlen（world）; 
 //但这不是合法的：
 len + = 2; //错误：len是const。 
  

2const char a + const char * b添加两个指针不是两个字符串，结果将是字符串a的地址加上字符串b的地址，其总和将是一些随机存储器位置

I've tried many ways to do that, I got a void which is static and is on Console class i made, Void it self works fine:

Console::WriteLine(const char* msg)

On the other side, I got another const char* non static void which calls the Console::WriteLine void from It, I've been working on C# for around a year and on C# I can easily do something like this:

string a = "Start ";
string b = a + "End";

When i call this on C++, it gives me bunch of errors:

Player::Kill(const char* Message)
{
    Console::WriteLine("> " + Message + " <");
}

I've also tried the strcat thing and put, But it tells me to use strcat_s which doesn't really work, And also I've tried to do string instead of const char*, And tried char*, But all of them give errors for the thing I'm trying to do.

解决方案

"const" means "cannot be changed(*1)". So you cannot simply "add" one const char string to another (*2). What you can do is copy them into a non-const character buffer.

const char* a = ...;
const char* b = ...;

char buffer[256]; // <- danger, only storage for 256 characters.
strncpy(buffer, a, sizeof(buffer));
strncat(buffer, b, sizeof(buffer));

// now buffer has the two strings joined together.

Your attempt to use std::string failed for a similar reason. You said:

std::string a = "Start";
std::string b = a + " End";

This translates to

b = (std::string)a + (const char*)" End";

Which should be ok except that it creates an extra string, what you probably wanted is

std::string a = "Start";
a += " End";

If you are getting compile errors doing this, please post them (Make sure you #include ).

Or you could do something like:

std::string addTwoStrings(const std::string& a, const std::string& b)
{
    return a + b; // works because they are both strings.
}

All of the following work: (see live demo http://ideone.com/Ytohgs)

#include <iostream>
#include <string>

std::string addTwoStrings(const std::string& a, const std::string& b)
{
    return a + b; // works because they are both strings.
}

void foo(const char* a, const char* b)
{
    std::string str = a;
    std::cout << "1st str = [" << str << "]" << std::endl;
    str += " ";
    std::cout << "2nd str = [" << str << "]" << std::endl;
    str += b;
    std::cout << "3rd str = [" << str << "]" << std::endl;
    str = addTwoStrings(a, " ");
    std::cout << "4th str = [" << str << "]" << std::endl;
    str = addTwoStrings(str, b);
    std::cout << "5th str = [" << str << "]" << std::endl;
}

int main()
{
    foo("hello", "world");
}

*1 Or more accurately, "cannot be changed in-situ" - you can use it in expressions, etc, so for example, e.g.

const size_t len = strlen("hello");
size_t newLen = len + strlen("world");
// but this would not be legal:
len += 2; // error: len is const.

2 "const char a + const char* b" is actually trying to add two pointers not two strings, the result would be the address of string a plus the address of string b, the sum of which would be some random memory location

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