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Difference between revisions of "cpp/string/wide/wmemcmp"

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< cpp‎ | string‎ | wide
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{{cpp/title|wmemcmp}}
 
{{cpp/title|wmemcmp}}
 
{{cpp/string/wide/navbar}}
 
{{cpp/string/wide/navbar}}
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{{ddcl | header=cwchar |
+
{{ddcl|header=cwchar|
 
int wmemcmp( const wchar_t* lhs, const wchar_t* rhs, std::size_t count );
 
int wmemcmp( const wchar_t* lhs, const wchar_t* rhs, std::size_t count );
 
}}
 
}}
  
−
Compares the first {{tt|count}} wide characters of the objects pointed to by {{tt|lhs}} and {{tt|rhs}}. The comparison is done lexicographically.
+
Compares the first {{c|count}} wide characters of the wide character arrays pointed to by {{c|lhs}} and {{c|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 {{c|count}} is zero, the function does nothing.
  
 
===Parameters===
 
===Parameters===
−
{{param list begin}}
+
{{par begin}}
−
{{param list item | lhs, rhs | pointers to the memory buffers to compare}}
+
{{par|lhs, rhs|pointers to the wide character arrays to compare}}
−
{{param list item | count | number of bytes to examine}}
+
{{par|count|number of wide characters to examine}}
−
{{param list end}}
+
{{par end}}
  
 
===Return value===
 
===Return value===
−
Negative value if {{tt|lhs}} is ''less than'' {{tt|rhs}}.
+
Negative value if the value of the first differing wide character in {{c|lhs}} is less than the value of the corresponding wide character in {{c|rhs}}: {{c|lhs}} precedes {{c|rhs}} in lexicographical order.
  
−
{{c|0}} if {{tt|lhs}} is ''equal to'' {{tt|rhs}}.
+
{{c|0}} if all {{c|count}} wide characters of {{c|lhs}} and {{c|rhs}} are equal.
  
−
Positive value if {{tt|lhs}} is ''greater than'' {{tt|rhs}}.
+
Positive value if the value of the first differing wide character in {{c|lhs}} is greater than the value of the corresponding wide character in {{c|rhs}}: {{c|rhs}} precedes {{c|lhs}} in lexicographical order.
 +
 
 +
===Notes===
 +
This function is not locale-sensitive and pays no attention to the values of the {{c|wchar_t}} objects it examines: nulls as well as invalid wide characters are compared too.
  
 
===Example===
 
===Example===
 
{{example
 
{{example
−
|
+
|code=
−
| code=
+
#include <clocale>
−
| output=
+
#include <cwchar>
 +
#include <iostream>
 +
#include <locale>
 +
#include <string>
 +
 
 +
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);
 +
}
 +
|p=true
 +
|output=
 +
αβγ precedes αβδ in lexicographical order
 +
αβδ follows αβγ in lexicographical order
 +
αβγ compares equal to αβγ in lexicographical order
 
}}
 
}}
  
 
===See also===
 
===See also===
−
{{dcl list begin}}
+
{{dsc begin}}
−
{{dcl list template | cpp/string/wide/dcl list wcscmp}}
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{{dsc inc|cpp/string/wide/dsc wcscmp}}
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{{dcl list template | cpp/string/wide/dcl list wcsncmp}}
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{{dsc inc|cpp/string/byte/dsc memcmp}}
−
{{dcl list see c | c/string/wide/wmemcmp}}
+
{{dsc inc|cpp/string/wide/dsc wcsncmp}}
−
{{dcl list end}}
+
{{dsc see c|c/string/wide/wmemcmp}}
 +
{{dsc end}}
 +
 
 +
{{langlinks|de|es|fr|it|ja|pt|ru|zh}}

Latest revision as of 11:14, 10 June 2023

 
C++
 
Strings library
 
Null-terminated wide strings
 
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.

Contents

[edit] Parameters

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

[edit] 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.

[edit] 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.

[edit] Example

Run this code
#include <clocale>
#include <cwchar>
#include <iostream>
#include <locale>
#include <string>
 
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

[edit] See also

 compares two wide strings
(function) [edit]
compares two buffers
(function) [edit]
compares a certain amount of characters from two wide strings
(function) [edit]
C documentation for wmemcmp
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