get_environment_from_os.cpp File Reference

#include <corecrt_internal.h>
#include <corecrt_internal_traits.h>
#include <stdlib.h>

Include dependency graph for get_environment_from_os.cpp:

Go to the source code of this file.

Classes
struct	anonymous_namespace{get_environment_from_os.cpp}::environment_strings_traits

Namespaces
namespace	anonymous_namespace{get_environment_from_os.cpp}

Typedefs
typedef __crt_unique_handle_t< environment_strings_traits >	anonymous_namespace{get_environment_from_os.cpp}::environment_strings_handle

Functions
static wchar_t const *__cdecl	find_end_of_double_null_terminated_sequence (wchar_t const *const first) throw ()
wchar_t *__cdecl	__dcrt_get_wide_environment_from_os () throw ()
char *__cdecl	__dcrt_get_narrow_environment_from_os () throw ()

Function Documentation

__dcrt_get_narrow_environment_from_os()

char *__cdecl __dcrt_get_narrow_environment_from_os	(	void		)
throw	(
	)

Definition at line 75 of file get_environment_from_os.cpp.

{
    // Note that we call GetEnvironmentStringsW and convert to multibyte.  The
    // GetEnvironmentStringsA function returns the environment in the OEM code
    // page, but we need the strings in ANSI.
    environment_strings_handle const environment(GetEnvironmentStringsW());
    if (!environment.is_valid())
        return nullptr;
 
    wchar_t const* const first = environment.get();
    wchar_t const* const last = find_end_of_double_null_terminated_sequence(first);
 
    size_t const required_wide_count = last - first;
#pragma warning(suppress:__WARNING_W2A_BEST_FIT) // 38021 Prefast recommends WC_NO_BEST_FIT_CHARS.
    size_t const required_narrow_count = static_cast<size_t>(__acrt_WideCharToMultiByte(
        CP_ACP,
        0,
        environment.get(),
        static_cast<int>(required_wide_count),
        nullptr,
        0,
        nullptr,
        nullptr));
 
    if (required_narrow_count == 0)
        return nullptr;
 
    __crt_unique_heap_ptr<char> buffer(_malloc_crt_t(char, required_narrow_count));
    if (!buffer)
        return nullptr;
 
#pragma warning(suppress:__WARNING_W2A_BEST_FIT) // 38021 Prefast recommends WC_NO_BEST_FIT_CHARS.
    int const conversion_result = __acrt_WideCharToMultiByte(
        CP_ACP,
        0,
        environment.get(),
        static_cast<int>(required_wide_count),
        buffer.get(),
        static_cast<int>(required_narrow_count),
        nullptr,
        nullptr);
 
    if (conversion_result == 0)
        return nullptr;
 
    return buffer.detach();
}

__dcrt_get_wide_environment_from_os()

wchar_t *__cdecl __dcrt_get_wide_environment_from_os	(	void		)
throw	(
	)

Definition at line 52 of file get_environment_from_os.cpp.

{
    environment_strings_handle const environment(GetEnvironmentStringsW());
    if (!environment)
        return nullptr;
 
    // Find the
    wchar_t const* const first = environment.get();
    wchar_t const* const last = find_end_of_double_null_terminated_sequence(first);
 
    size_t const required_count = last - first;
 
    __crt_unique_heap_ptr<wchar_t> buffer(_malloc_crt_t(wchar_t, required_count));
    if (!buffer)
        return nullptr;
 
    // Note that the multiplication here cannot overflow:
    memcpy(buffer.get(), environment.get(), required_count * sizeof(wchar_t));
    return buffer.detach();
}

find_end_of_double_null_terminated_sequence()

static wchar_t const *__cdecl find_end_of_double_null_terminated_sequence ( wchar_t const *const  first ) throw ( )

static

Definition at line 40 of file get_environment_from_os.cpp.

{
    wchar_t const* last = first;
    for (; *last != '\0'; last += wcslen(last) + 1)
    {
    }
 
    return last + 1; // Return the pointer one-past-the-end of the double null terminator
}

Referenced by __dcrt_get_narrow_environment_from_os(), and __dcrt_get_wide_environment_from_os().