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memcmp

From cppreference.com
< c‎ | string‎ | byte
Defined in header <string.h>
int memcmp( const void* lhs, const void* rhs, size_t count );

Compares the first count characters of the objects 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 bytes (both interpreted as unsigned char) that differ in the objects being compared.

Contents

[edit] Parameters

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

[edit] Return value

Negative value if lhs appears before rhs in lexicographical order.

Zero if lhs and rhs compare equal.

Positive value if lhs appears after rhs in lexicographical order.

[edit] Notes

This function reads object representations, not the object values, and is typically meaningful for byte arrays only: structs may have padding bytes whose values are indeterminate.

[edit] Example

#include <stdio.h>
#include <string.h>
 
void demo(const char* lhs, const char* rhs, size_t sz)
{
    for(size_t n = 0; n < sz; ++n) putchar(lhs[n]);
    int rc = memcmp(lhs, rhs, sz);
    if(rc == 0)
        printf(" compares equal to ");
    else if(rc < 0)
        printf(" precedes ");
    else if(rc > 0)
        printf(" follows ");
    for(size_t n = 0; n < sz; ++n) putchar(rhs[n]);
    puts(" in lexicographical order");
}
 
int main(void)
{
    char a1[] = {'a','b','c'};
    char a2[sizeof a1] = {'a','b','d'};
 
    demo(a1, a2, sizeof a1);
    demo(a2, a1, sizeof a1);
    demo(a1, a1, sizeof a1);
}

Output:

abc precedes abd in lexicographical order
abd follows abc in lexicographical order
abc compares equal to abc in lexicographical order

[edit] References

  • C11 standard (ISO/IEC 9899:2011):
  • 7.24.4.1 The memcmp function (p: 365)
  • C99 standard (ISO/IEC 9899:1999):
  • 7.21.4.1 The memcmp function (p: 328)
  • C89/C90 standard (ISO/IEC 9899:1990):

[edit] See also

compares two strings
(function) [edit]
compares a certain amount of characters of two strings
(function) [edit]