我正在研究一些旧的(并且专门面向 win32 的)东西,并考虑使其更加现代/可移植 - 即在 C++11 中重新实现一些广泛可重用的部分。其中之一是 utf8 和 utf16 之间的转换。在我使用的 Win32 API 中MultiByteToWideChar
/WideCharToMultiByte
,尝试使用此处的示例代码将这些内容移植到 C++11:https://stackoverflow.com/a/14809553 https://stackoverflow.com/a/14809553。结果是
发布版本(由MSVS 2013编译,在Core i7 3610QM上运行)
stdlib = 1587.2 ms
Win32 = 127.2 ms
调试构建
stdlib = 5733.8 ms
Win32 = 127.2 ms
问题是- 代码有问题吗?如果一切似乎都正常——这种性能差异有什么充分的理由吗?
测试代码如下:
#include <iostream>
#include <fstream>
#include <string>
#include <iterator>
#include <clocale>
#include <codecvt>
#define XU_BEGIN_TIMER(NAME) \
{ \
LARGE_INTEGER __freq; \
LARGE_INTEGER __t0; \
LARGE_INTEGER __t1; \
double __tms; \
const char* __tname = NAME; \
char __tbuf[0xff]; \
\
QueryPerformanceFrequency(&__freq); \
QueryPerformanceCounter(&__t0);
#define XU_END_TIMER() \
QueryPerformanceCounter(&__t1); \
__tms = (__t1.QuadPart - __t0.QuadPart) * 1000.0 / __freq.QuadPart; \
sprintf_s(__tbuf, sizeof(__tbuf), " %-24s = %6.1f ms\n", __tname, __tms ); \
OutputDebugStringA(__tbuf); \
printf(__tbuf); \
}
std::string read_utf8() {
std::ifstream infile("C:/temp/UTF-8-demo.txt");
std::string fileData((std::istreambuf_iterator<char>(infile)),
std::istreambuf_iterator<char>());
infile.close();
return fileData;
}
void testMethod() {
std::setlocale(LC_ALL, "en_US.UTF-8");
std::string source = read_utf8();
{
std::string utf8;
XU_BEGIN_TIMER("stdlib") {
for( int i = 0; i < 1000; i++ ) {
std::wstring_convert<std::codecvt_utf8_utf16<char16_t>, char16_t> convert2utf16;
std::u16string utf16 = convert2utf16.from_bytes(source);
std::wstring_convert<std::codecvt_utf8_utf16<char16_t>, char16_t> convert2utf8;
utf8 = convert2utf8.to_bytes(utf16);
}
} XU_END_TIMER();
FILE* output = fopen("c:\\temp\\utf8-std.dat", "wb");
fwrite(utf8.c_str(), 1, utf8.length(), output);
fclose(output);
}
char* utf8 = NULL;
int cchA = 0;
{
XU_BEGIN_TIMER("Win32") {
for( int i = 0; i < 1000; i++ ) {
WCHAR* utf16 = new WCHAR[source.length() + 1];
int cchW;
utf8 = new char[source.length() + 1];
cchW = MultiByteToWideChar(
CP_UTF8, 0, source.c_str(), source.length(),
utf16, source.length() + 1);
cchA = WideCharToMultiByte(
CP_UTF8, 0, utf16, cchW,
utf8, source.length() + 1, NULL, false);
delete[] utf16;
if( i != 999 )
delete[] utf8;
}
} XU_END_TIMER();
FILE* output = fopen("c:\\temp\\utf8-win.dat", "wb");
fwrite(utf8, 1, cchA, output);
fclose(output);
delete[] utf8;
}
}