标签： 面试题

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float fs[] = { 1.1f, 2.2f, 3.3f, 4.4f, 5.5f };
double ds[] = { 1.1, 2.2, 3.3, 4.4, 5.5 };
DWORD tk = ::GetTickCount ();
float f = 0.0f;
for (int i = 0; i < 100000000; ++i) {
    f += fs[i % 5];
}
tk = ::GetTickCount () - tk;
std::cout << "float:" << f << "    " << tk << '\n';
tk = ::GetTickCount ();
double d = 0.0;
for (int i = 0; i < 100000000; ++i) {
    d += ds[i % 5];
}
tk = ::GetTickCount () - tk;
std::cout << "double:" << d << "    " << tk << '\n';

float fs[] = { 1.1f, 2.2f, 3.3f, 4.4f, 5.5f }; double ds[] = { 1.1, 2.2, 3.3, 4.4, 5.5 }; DWORD tk = ::GetTickCount (); float f = 0.0f; for (int i = 0; i < 100000000; ++i) { f += fs[i % 5]; } tk = ::GetTickCount () - tk; std::cout << "float:" << f << " " << tk << '\n'; tk = ::GetTickCount (); double d = 0.0; for (int i = 0; i < 100000000; ++i) { d += ds[i % 5]; } tk = ::GetTickCount () - tk; std::cout << "double:" << d << " " << tk << '\n';

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char a[256][256], b[257][257]; // 全局变量
DWORD tk = ::GetTickCount ();
for (int i = 0; i < 256; ++i)
    for (int j = 0; j < 256; ++j)
        for (int k = 0; k < 10000; ++k)
            a[i][j] += '\x01';
tk = ::GetTickCount () - tk;
std::cout << "256:" << tk << '\n';
tk = ::GetTickCount ();
for (int i = 0; i < 257; ++i)
    for (int j = 0; j < 257; ++j)
        for (int k = 0; k < 10000; ++k)
            b[i][j] += '\x01';
tk = ::GetTickCount () - tk;
std::cout << "257:" << tk << '\n';

char a[256][256], b[257][257]; // 全局变量 DWORD tk = ::GetTickCount (); for (int i = 0; i < 256; ++i) for (int j = 0; j < 256; ++j) for (int k = 0; k < 10000; ++k) a[i][j] += '\x01'; tk = ::GetTickCount () - tk; std::cout << "256:" << tk << '\n'; tk = ::GetTickCount (); for (int i = 0; i < 257; ++i) for (int j = 0; j < 257; ++j) for (int k = 0; k < 10000; ++k) b[i][j] += '\x01'; tk = ::GetTickCount () - tk; std::cout << "257:" << tk << '\n';

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std::string a = "hello";
std::string b = a;
std::cout << (a.c_str () == b.c_str () ? "true" : "false") << '\n';
char ch = b[0];
std::cout << (a.c_str () == b.c_str () ? "true" : "false") << '\n';
a = "";
std::cout << (a.c_str () == b.c_str () ? "true" : "false") << '\n';

std::string a = "hello"; std::string b = a; std::cout << (a.c_str () == b.c_str () ? "true" : "false") << '\n'; char ch = b[0]; std::cout << (a.c_str () == b.c_str () ? "true" : "false") << '\n'; a = ""; std::cout << (a.c_str () == b.c_str () ? "true" : "false") << '\n';