How Long Does the `std::string::c_str()` Pointer Remain Valid?

Understanding the Lifetime of std::string::c_str()

In programming, interfacing with legacy code that operates with const char variables can present challenges, especially when your application primarily employs std::string objects. Accessing the underlying const char data of an std::string instance through c_str() can fulfill this requirement, but it introduces concerns regarding the result's lifetime.

When utilizing c_str(), it's imperative to comprehend the duration of its returned value. The c_str() result becomes invalid if the std::string it derives from is destroyed or if a non-const function of the string is invoked. Therefore, preserving the c_str() result often requires creating a copy.

Consider the following code snippet:

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

In this example, the c_str() results are used within a limited scope, where the corresponding std::string objects remain intact. As a result, the c_str() values are considered valid throughout the execution of this block. However, external functions invoked through pointers (such as use_foo()) or destructors (~Foo()) may affect the validity of these c_str() results.

To ensure the safe use of c_str() results, it's generally recommended to create a separate copy if you intend to store them beyond the lifetime of the original std::string objects. This ensures the preservation of the underlying data and mitigates the risk of undefined behavior.

The above is the detailed content of How Long Does the `std::string::c_str()` Pointer Remain Valid?. For more information, please follow other related articles on the PHP Chinese website!