是const_cast安全吗? [英] Is const_cast safe?
问题描述
我找不到很多关于const_cast的信息。我可以找到(在堆栈溢出)的唯一信息是:
const_cast <>()用于添加/删除const )(或波动性)。
这让我很紧张。可以使用const_cast引起意外的行为?
或者,什么时候可以使用const_cast? div <>> const_cast
是安全的,只有当你转换一个最初非 - const
的变量。例如,如果你有一个函数接受 const char *
的参数,并且传递一个可修改的 char *
,可以安全地将 const_cast
该参数返回到 char *
并修改它。但是,如果原始变量实际上 const
,则使用 const_cast
将导致未定义的行为。
void func(const char * param,size_t sz,bool modify)
{
if(modify)
strncpy(const_cast< char *>(param),sz,new string);
printf(param:%s\\\
,param);
}
...
char缓冲区[16];
const char * unmodifiable =string constant;
func(buffer,sizeof(buffer),true); // OK
func(unmodifiable,strlen(unmodifiable),false); // OK
func(unmodifiable,strlen(unmodifiable),true); // UNDEFINED BEHAVIOR
I can't find much information on const_cast. The only info I could find (on Stack Overflow) is:
The const_cast<>() is used to add/remove const(ness) (or volatile-ness) of a variable.
This makes me nervous. Could using a const_cast cause unexpected behavior? If so, what?
Alternatively, when is it okay to use const_cast?
const_cast
is safe only if you're casting a variable that was originally non-const
. For example, if you have a function that takes a parameter of a const char *
, and you pass in a modifiable char *
, it's safe to const_cast
that parameter back to a char *
and modify it. However, if the original variable was in fact const
, then using const_cast
will result in undefined behavior.
void func(const char *param, size_t sz, bool modify)
{
if(modify)
strncpy(const_cast<char *>(param), sz, "new string");
printf("param: %s\n", param);
}
...
char buffer[16];
const char *unmodifiable = "string constant";
func(buffer, sizeof(buffer), true); // OK
func(unmodifiable, strlen(unmodifiable), false); // OK
func(unmodifiable, strlen(unmodifiable), true); // UNDEFINED BEHAVIOR
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