std::wmemcmp

 

C++

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Technical Specifications

 

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Null-terminated wide strings

Functions
Character manipulation
iswalnum iswalpha iswlower iswupper iswdigit iswxdigit iswblank (C++11) wctype iswctype	iswcntrl iswgraph iswspace iswprint iswpunct towlower towupper wctrans towctrans
Conversions to numeric formats
wcstolwcstoll wcstoulwcstoull	wcstofwcstodwcstold wcstoimaxwcstouimax (C++11)(C++11)
String manipulation
wcslen wcscpy wcsncpy wcscat wcsncat wcscmp wcscoll wcsncmp	wcsxfrm wcschr wcsrchr wcspbrk wcsspn wcscspn wcsstr wcstok
Array manipulation
wmemcpy
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wmemcmp
wmemchr
wmemset

 

Defined in header <cwchar>
int wmemcmp( const wchar_t* lhs, const wchar_t* rhs, std::size_t count );

Compares the first count wide characters of the wide character arrays pointed to by lhs and rhs. The comparison is done lexicographically.

The sign of the result is the sign of the difference between the values of the first pair of wide characters that differ in the arrays being compared.

If count is zero, the function does nothing.

Parameters

lhs, rhs	-	pointers to the wide character arrays to compare
count	-	number of wide characters to examine

Return value

Negative value if the value of the first differing wide character in lhs is less than the value of the corresponding wide character in rhs: lhs precedes rhs in lexicographical order.

​0​ if all count wide characters of lhs and rhs are equal.

Positive value if the value of the first differing wide character in lhs is greater than the value of the corresponding wide character in rhs: rhs precedes lhs in lexicographical order.

Notes

This function is not locale-sensitive and pays no attention to the values of the wchar_t objects it examines: nulls as well as invalid wide characters are compared too.

Example

Run this code

#include <iostream>
#include <string>
#include <cwchar>
#include <locale>
#include <clocale>
 
void demo(const wchar_t* lhs, const wchar_t* rhs, std::size_t sz)
{
    std::wcout << std::wstring(lhs, sz);
    int rc = std::wmemcmp(lhs, rhs, sz);
    if(rc == 0)
        std::wcout << " compares equal to ";
    else if(rc < 0)
        std::wcout << " precedes ";
    else if(rc > 0)
        std::wcout << " follows ";
    std::wcout << std::wstring(rhs, sz) << " in lexicographical order\n";
}
 
int main()
{
    std::setlocale(LC_ALL, "en_US.utf8");
    std::wcout.imbue(std::locale("en_US.utf8"));
 
    wchar_t a1[] = {L'α',L'β',L'γ'};
    constexpr std::size_t sz = sizeof a1 / sizeof *a1;
    wchar_t a2[sz] = {L'α',L'β',L'δ'};
 
    demo(a1, a2, sz);
    demo(a2, a1, sz);
    demo(a1, a1, sz);
}

Possible output:

αβγ precedes αβδ in lexicographical order
αβδ follows αβγ in lexicographical order
αβγ compares equal to αβγ in lexicographical order

See also

wcscmp	compares two wide strings (function)
memcmp	compares two buffers (function)
wcsncmp	compares a certain amount of characters from two wide strings (function)
C documentation for wmemcmp