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strncmp

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

Compares at most count characters of two null-terminated byte strings. The comparison is done lexicographically.

The sign of the result is the sign of the difference between the values of the first pair of characters (both interpreted as unsigned char) that differ in the strings being compared.

The behavior is undefined if lhs or rhs are not pointers to null-terminated strings.

Contents

[edit] Parameters

lhs, rhs - pointers to the null-terminated byte strings to compare
count - maximum number of characters to compare

[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] Example

#include <string.h>
#include <stdio.h>
 
void demo(const char* lhs, const char* rhs, int sz)
{
    int rc = strncmp(lhs, rhs, sz);
    if(rc == 0)
        printf("First %d chars of [%s] equal [%s]\n", sz, lhs, rhs);
    else if(rc < 0)
        printf("First %d chars of [%s] precede [%s]\n", sz, lhs, rhs);
    else if(rc > 0)
        printf("First %d chars of [%s] follow [%s]\n", sz, lhs, rhs);
 
}
int main(void)
{
    const char* string = "Hello World!";
    demo(string, "Hello!", 5);
    demo(string, "Hello", 10);
    demo(string, "Hello there", 10);
    demo("Hello, everybody!" + 12, "Hello, somebody!" + 11, 5);
}

Output:

First 5 chars of [Hello World!] equal [Hello!]
First 10 chars of [Hello World!] follow [Hello]
First 10 chars of [Hello World!] precede [Hello there]
First 5 chars of [body!] equal [body!]

[edit] References

  • C11 standard (ISO/IEC 9899:2011):
  • 7.24.4.4 The strncmp function (p: 366)
  • C99 standard (ISO/IEC 9899:1999):
  • 7.21.4.4 The strncmp function (p: 329)
  • C89/C90 standard (ISO/IEC 9899:1990):

[edit] See also

compares two strings
(function) [edit]
compares a certain amount of characters from two wide strings
(function) [edit]
compares two buffers
(function) [edit]
compares two strings in accordance to the current locale
(function) [edit]
C++ documentation for strncmp