std::memcmp

 

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Defined in header <cstring>
int memcmp( const void* lhs, const void* rhs, std::size_t count );

Reinterprets the objects pointed to by lhs and rhs as arrays of unsigned char and compares the first count characters of these arrays. The comparison is done lexicographically.

Parameters

lhs, rhs	-	pointers to the memory buffers to compare
count	-	number of bytes to examine

Return value

Negative value if the first differing byte (reinterpreted as unsigned char) in lhs is less than the corresponding byte in rhs.

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

Positive value if the first differing byte in lhs is greater than the corresponding byte in rhs.

Notes

This function reads object representations, not the object values, and is typically meaningful for trivially-copyable objects only. For example, memcmp() between two objects of type std::string or std::vector will not compare their contents.

Example

Run this code

#include <iostream>
#include <cstring>
 
int main()
{
    char a1[] = {'a', 'b', 'c'};
    char a2[] = {'a', 'b', 'd'};
 
    std::cout << "'abc' vs 'abd': " << std::memcmp(a1, a2, sizeof a1) << '\n'
              << "'abd' vs 'abc': " << std::memcmp(a2, a1, sizeof a1) << '\n'
              << "'abc' vs 'abc': " << std::memcmp(a1, a1, sizeof a1) << '\n';
}

Output:

'abc' vs 'abd': -1
'abd' vs 'abc': 1
'abc' vs 'abc': 0

See also

strcmp	compares two strings (function)
strncmp	compares a certain number of characters from two strings (function)
C documentation for memcmp