什么是std :: string :: c_str()生存期? [英] What is std::string::c_str() lifetime?
问题描述
在我的一个程序中,我必须使用 const char *
来处理一些旧代码。
In one of my programs, I have to interface with some legacy code that works with const char*
.
假设我有一个如下的结构:
Lets say I have a structure which looks like:
struct Foo
{
const char* server;
const char* name;
};
我的高级应用程序只处理 std :: string
,所以我想到使用 std :: string :: c_str()
回到 const char *
指针。
My higher-level application only deals with std::string
, so I thought of using std::string::c_str()
to get back const char*
pointers.
但是 c_str()的生命周期是什么?
?
我可以这样做,而不面对未定义的行为吗?
Can I do something like this without facing undefined behavior ?
{
std::string server = "my_server";
std::string name = "my_name";
Foo foo;
foo.server = server.c_str();
foo.name = name.c_str();
// We use foo
use_foo(foo);
// Foo is about to be destroyed, before name and server
}
还是我应该立即将 c_str()
的结果复制到另一个地方?
Or am I supposed to immediately copy the result of c_str()
to another place ?
谢谢。
推荐答案
c_str()
std :: string
被销毁或者如果字符串的非const成员函数被调用。所以,通常你会想要它的副本,如果你需要保持它。
The c_str()
result becomes invalid if the std::string
is destroyed or if a non-const member function of the string is called. So, usually you will want to make a copy of it if you need to keep it around.
在你的例子的情况下,看起来的结果 c_str()
被安全地使用,因为在该范围内的字符串不被修改。 (但是,我们不知道 use_foo()
或〜Foo()
如果他们将字符串复制到其他地方,那么他们应该做一个真正的复制,而不是只复制 char
指针。)
In the case of your example, it appears that the results of c_str()
are used safely, because the strings are not modified while in that scope. (However, we don't know what use_foo()
or ~Foo()
might be doing with those values; if they copy the strings elsewhere, then they should do a true copy, and not just copy the char
pointers.)
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