memchr

 

C

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Technical Specifications

Symbol index

 

Strings library

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Functions
Character manipulation
isalnum isalpha islower isupper isdigit isxdigit isblank (C99)	iscntrl isgraph isspace isprint ispunct tolower toupper
Conversions to and from numeric formats
atoiatolatoll (C99) atof strtolstrtoll (C99) strtoulstrtoull (C99)	strtoimaxstrtoumax (C99)(C99) strtofstrtodstrtold (C99)(C99) strfromfstrfromdstrfromld (C23)(C23)(C23)
String manipulation
strcpystrcpy_s (C11) strncpystrncpy_s (C11) strcatstrcat_s (C11)	strncatstrncat_s (C11) strxfrm strdup (C23) strndup (C23)
String examination
strlenstrnlen_s (C11) strcmp strncmp strcoll strchr strrchr	strspn strcspn strpbrk strstr strtokstrtok_s (C11)
Memory manipulation
memchr memcmp memsetmemset_explicitmemset_s (C23)(C11)	memcpymemcpy_s (C11) memmovememmove_s (C11) memccpy (C23)
Miscellaneous
strerrorstrerror_sstrerrorlen_s (C11)(C11)

 

Defined in header <string.h>
void *memchr( const void *ptr, int ch, size_t count );	(1)
/*QVoid*/ *memchr( /*QVoid*/ *ptr, int ch, size_t count );	(2)	(since C23)

1) Finds the first occurrence of (unsigned char)ch in the initial count bytes (each interpreted as unsigned char) of the object pointed to by ptr.

2) Type-generic function equivalent to (1). Let T be an unqualified object type (including void).

• If ptr is of type const T*, the return type is const void*.
• Otherwise, if ptr is of type T*, the return type is void*.
• Otherwise, the behavior is undefined.

If a macro definition of each of these generic functions is suppressed to access an actual function (e.g. if (memchr) or a function pointer is used), the actual function declaration (1) becomes visible.

The behavior is undefined if access occurs beyond the end of the array searched. The behavior is undefined if ptr is a null pointer.

This function behaves as if it reads the bytes sequentially and stops as soon as a matching bytes is found: if the array pointed to by ptr is smaller than count, but the match is found within the array, the behavior is well-defined

(since C11)

Parameters

ptr	-	pointer to the object to be examined
ch	-	bytes to search for
count	-	max number of bytes to examine

Return value

Pointer to the location of the byte, or a null pointer if no such byte is found.

Example

Run this code

#include <stdio.h>
#include <string.h>
 
int main(void)
{
    const char str[] = "ABCDEFG";
    const int chars[] = {'D', 'd'};
    for (size_t i = 0; i < sizeof chars / (sizeof chars[0]); ++i)
    {
        const int c = chars[i];   
        const char *ps = memchr(str, c, strlen(str));
        ps ? printf ("character '%c'(%i) found: %s\n", c, c, ps)
           : printf ("character '%c'(%i) not found\n", c, c);
    }
    return 0;
}

Possible output:

character 'D'(68) found: DEFG
character 'd'(100) not found

References

• C17 standard (ISO/IEC 9899:2018):

• 7.24.5.1 The memchr function (p: 267-268)

• C11 standard (ISO/IEC 9899:2011):

• 7.24.5.1 The memchr function (p: 367)

• C99 standard (ISO/IEC 9899:1999):

• 7.21.5.1 The memchr function (p: 330)

• C89/C90 standard (ISO/IEC 9899:1990):

• 4.11.5.1 The memchr function

See also

strchr

finds the first occurrence of a character (function)