“localtime_s”：不是 VS2015 中“std”的成员

Question

The following C++ code does not compile with VS2015:

#include <time.h>
#include <ctime>

void main()
{
    const time_t t = std::time(nullptr);

    std::tm tm = {};

    std::localtime_s(&tm, &time);
}

The error messages are:

Microsoft (R) C/C++ Optimizing Compiler Version 19.00.24215.1 for x86 Copyright (C) Microsoft Corporation. All rights reserved.

t.cpp t.cpp(10): error C2039: 'localtime_s': is not a member of 'std' C:\\Program Files (x86)\\Microsoft Visual Studio 14.0\\VC\\INCLUDE\\ctime(17): note: see declaration of 'std' t.cpp(10): error C2664: 'errno_t localtime_s(tm *const ,const time_t *const )': cannot convert argument 2 from 'time_t (__cdecl *)(time_t *const )' to 'const time_t *const ' t.cpp(10): note: There is no context in which this conversion is possible

What can be a workaround? (using std::localtime() is not an option).

Answer 1

Per [headers]/10

Annex K of the C standard describes a large number of functions, with associated types and macros, which “promote safer, more secure programming” than many of the traditional C library functions. The names of the functions have a suffix of _s; most of them provide the same service as the C library function with the unsuffixed name, but generally take an additional argument whose value is the size of the result array. If any C++ header is included, it is implementation-defined whether any of these names is declared in the global namespace. (None of them is declared in namespace std.)

^{Emphasis mine}

and table 18 list localtime_s as a member so, because of the above section, we know that it is not defined in namespace std and if it does exist it will be in the global namespace. Try using

::localtime_s(&tm, &time);

and if that still does not work it means your implementation does not support it.