C代码表现得很奇怪。 [英] C code behaving strangely.

问题描述

#include<iostream>
using namespace std ; 

int main ()
{
  char *c = new char(100);

strcpy( c , (char*)"http://localhost:4000/index.html") ; 


strcpy ( c, &c[6] ) ;

printf(" url is %s\n" , c  ) ; 

return 0 ;

}

此代码输出：

url是/ localhost：ndex .htmlx.html



我的尝试：

This code outputs :
url is /localhost:ndex.htmlx.html

What I have tried:

I wanted to output /localhost:4000/index.html. I know that this can be done through assigning c = c+ 6 but I want to know how does the above code works ? 
Where does the number 4000 disappear and from where does the extra stuff comes from ?

推荐答案

引用：

strcpy（c，& c [6]）;

strcpy ( c, &c[6] ) ;

在上面一行中你误用 strcpy 。

来自文档 [ ^ ]：

In the above line you are misusing strcpy.
From the documentation[^]:

为避免溢出，目标指向的数组大小应足够长，以包含与源相同的C字符串（包括终止空字符），不应该在内存中与源重叠。

To avoid overflows, the size of the array pointed by destination shall be long enough to contain the same C string as source (including the terminating null character), and should not overlap in memory with source.

使用source重叠目标就是你正在做的事情。





请注意，您的代码是 C 和<$ c $的奇怪组合C> C ++ 。您可以随时使用 C ++ 编译器编写：

Overlapping destination with source is just what you are doing.


Please note, your code is an odd mix of C and C++. Having at your disposal the C++ compiler, you might simply write:

#include <iostream>

int main ()
{
  const char * p = "http://localhost:4000/index.html";
  std::cout << (p+6) << "\n";
}

经验法则：你应该避免strcpy到它自己。您可以为参数使用2个不同的变量。这应该可以解决这种陌生感。

Rule of thumb: you should avoid strcpy to itself. You use 2 different variables for the parameters. That should solve the strangeness.

这并不奇怪，但按设计工作。反斜杠是一个特殊符号，在普通字符串中无效，但在下面标出一些特殊字符。



要正确处理它，你需要为每个单反斜杠添加第二个反斜杠。像那样：

This is NOT strange but "works as designed". The backslash is a special sign which isnt valid in plain strings but signals some special characters following.

To handle it correct you need to add a second backslash for EACH single backslash. Like that:

strcpy( c , (char*)"http:////localhost:4000//index.html") ;

读入维基百科获取更多见解。

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