`_lfind_s`

Artikel
12/02/2022

Performs a linear search for the specified key. A version of _lfind with security enhancements as described in Security features in the CRT.

Syntax

void *_lfind_s(
   const void *key,
   const void *base,
   unsigned int *num,
   size_t size,
   int (__cdecl *compare)(void *, const void *, const void *),
   void * context
);

Parameters

key
Object to search for.

base
Pointer to the base of search data.

number
Number of array elements.

size
Size of array elements in bytes.

compare
Pointer to comparison routine. The first parameter is the context pointer. The second parameter is a pointer to key for search. The third parameter is a pointer to array element to be compared with key.

context
A pointer to an object that might be accessed in the comparison function.

Return value

If the key is found, _lfind_s returns a pointer to the element of the array at base that matches key. If the key isn't found, _lfind_s returns NULL.

If invalid parameters are passed to the function, the invalid parameter handler is invoked, as described in Parameter validation. If execution is allowed to continue, errno is set to EINVAL and the function returns NULL.

Error conditions

`key`	`base`	`compare`	`number`	`size`	`errno`
`NULL`	any	any	any	any	`EINVAL`
any	`NULL`	any	!= 0	any	`EINVAL`
any	any	any	any	zero	`EINVAL`
any	any	`NULL`	an	any	`EINVAL`

Remarks

The _lfind_s function performs a linear search for the value key in an array of number elements, each of size bytes. Unlike bsearch_s, _lfind_s doesn't require the array to be sorted. The base argument is a pointer to the base of the array to be searched. The compare argument is a pointer to a user-supplied routine that compares two array elements and then returns a value specifying their relationship. _lfind_s calls the compare routine one or more times during the search, passing the context pointer and pointers to two array elements on each call. The compare routine must compare the elements then return nonzero (meaning that the elements are different) or 0 (meaning the elements are identical).

_lfind_s is similar to _lfind except for the addition of the context pointer to the arguments of the comparison function and the parameter list of the function. The context pointer can be useful if the searched data structure is part of an object and the compare function needs to access members of the object. The compare function can cast the void pointer into the appropriate object type and access members of that object. The addition of the context parameter makes _lfind_s more secure because extra context can be used to avoid reentrancy bugs associated with using static variables to make data available to the compare function.

By default, this function's global state is scoped to the application. To change this behavior, see Global state in the CRT.

Requirements

Routine	Required header
`_lfind_s`	<search.h>

For more compatibility information, see Compatibility.

Example

// crt_lfind_s.cpp
// This program uses _lfind_s to search a string array,
// passing a locale as the context.
// compile with: /EHsc
#include <stdlib.h>
#include <stdio.h>
#include <search.h>
#include <process.h>
#include <locale.h>
#include <locale>
#include <windows.h>
using namespace std;

// The sort order is dependent on the code page.  Use 'chcp' at the
// command line to change the codepage.  When executing this application,
// the command prompt codepage must match the codepage used here:

#define CODEPAGE_850

#ifdef CODEPAGE_850
// Codepage 850 is the OEM codepage used by the command line,
// so \x00e1 is the German Sharp S

char *array1[] = { "wei\x00e1", "weis", "annehmen", "weizen", "Zeit",
                   "weit" };

#define GERMAN_LOCALE "German_Germany.850"

#endif

#ifdef CODEPAGE_1252
   // If using codepage 1252 (ISO 8859-1, Latin-1), use \x00df
   // for the German Sharp S
char *array1[] = { "wei\x00df", "weis", "annehmen", "weizen", "Zeit",
                   "weit" };

#define GERMAN_LOCALE "German_Germany.1252"

#endif

// The context parameter lets you create a more generic compare.
// Without this parameter, you would have stored the locale in a
// static variable, thus making it vulnerable to thread conflicts
// (if this were a multithreaded program).

int compare( void *pvlocale, const void *str1, const void *str2)
{
    char *s1 = *(char**)str1;
    char *s2 = *(char**)str2;

    locale& loc = *( reinterpret_cast< locale * > ( pvlocale));

    return use_facet< collate<char> >(loc).compare(
       s1, s1+strlen(s1),
       s2, s2+strlen(s2) );
}

void find_it( char *key, char *array[], unsigned int num, locale &loc )
{
   char **result = (char **)_lfind_s( &key, array,
                      &num, sizeof(char *), compare, &loc );
   if( result )
      printf( "%s found\n", *result );
   else
      printf( "%s not found\n", key );
}

int main( )
{
   find_it( "weit", array1, sizeof(array1)/sizeof(char*), locale(GERMAN_LOCALE) );
}

weit found

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