keil不能使用strstr函数怎么办？
函数定义：
char *strx;
char MLSBUF[100];
出问题的代码：
strx = strstr((const char*)MLSBUF,(const char*)"OK");
引用的头文件：
#include "string.h"
#include "stdio.h"
具体问题：
查阅相关资料说是没有找到strstr函数的定义，然后我到string.h里面看了看，发现的确没有strstr函数定义，该怎么解决啊
string.h:
/*--------------------------------------------------------------------------
STRING.H
String functions for C251 Version 4.
Copyright (c) 1995-2007 Keil Elektronik GmbH and Keil Software, Inc.
All rights reserved.
--------------------------------------------------------------------------*/
#pragma SAVE
#pragma PARM251
#ifndef _SIZE_T
#define _SIZE_T
typedef unsigned int size_t;
#endif
#ifndef NULL
#define NULL ((void *) 0L)
#endif
#if (__C251__ >= 200)
extern char *strcat (char *s1, const char *s2) reentrant;
extern char *strncat (char *s1, const char *s2, size_t n) reentrant;
extern char strcmp (const char *s1, const char *s2) reentrant;
extern char strncmp (const char *s1, const char *s2, size_t n) reentrant;
extern char *strcpy (char *s1, const char *s2) reentrant;
extern char *strncpy (char *s1, const char *s2, size_t n) reentrant;
extern size_t strlen (const char *) reentrant;
extern char *strchr (const char *s, char c) reentrant;
extern int strpos (const char *s, char c) reentrant;
extern char *strrchr (const char *s, char c) reentrant;
extern int strrpos (const char *s, char c) reentrant;
extern size_t strspn (const char *s, const char *set) reentrant;
extern size_t strcspn (const char *s, const char *set) reentrant;
extern char *strpbrk (const char *s, const char *set) reentrant;
extern char *strrpbrk (const char *s, const char *set) reentrant;
extern char memcmp (const void *s1, const void *s2, size_t n) reentrant;
extern void *memcpy (void *s1, const void *s2, size_t n) reentrant;
extern void *memchr (const void *s, char val, size_t n) reentrant;
extern void *memccpy (void *s1, const void *s2, char val, size_t n) reentrant;
extern void *memmove (void *s1, const void *s2, size_t n) reentrant;
extern void *memset (void *s, char val, size_t n) reentrant;
extern void far *fmemset (void far *s, char val, unsigned int n) reentrant;
extern void xdata *xmemset (void xdata *s, char val, unsigned int n) reentrant;
extern void far *fmemcpy (void far *s1, void far *s2, unsigned int n) reentrant;
extern void xdata *xmemcpy (void xdata *s1, void xdata *s2, unsigned int n) reentrant;
extern unsigned long hstrlen (const char huge *s) reentrant;
extern char hstrcmp (const char huge *s1, const char huge *s2) reentrant;
extern char huge *hstrcpy (char huge *s1, const char huge *s2) reentrant;
#pragma PARM4 // allow a maximum of 4 long as register parameters
extern char huge *hstrncpy (char huge *s1, const char huge *s2, unsigned long n) reentrant;
extern char hmemcmp (const void huge *s1, const void huge *s2, unsigned long len) reentrant;
extern void huge *hmemcpy (void huge *s1, const void huge *s2, unsigned long len) reentrant;
extern void huge *hmemchr (const void huge *ptr, char val, unsigned long len) reentrant;
extern char huge *hmemccpy (char huge *dest, const char huge *src, char val, unsigned long len) reentrant;
extern void huge *hmemmove (void huge *s1, const void huge *s2, unsigned long len) reentrant;
extern void huge *hmemset (void huge *ptr, char val, unsigned long len) reentrant;
#else
extern char *strcat (char *s1, char *s2);
extern char *strncat (char *s1, char *s2, int n);
extern char strcmp (char *s1, char *s2);
extern char strncmp (char *s1, char *s2, int n);
extern char *strcpy (char *s1, char *s2);
extern char *strncpy (char *s1, char *s2, int n);
extern int strlen (char *);
extern char *strchr (const char *s, char c);
extern int strpos (const char *s, char c);
extern char *strrchr (const char *s, char c);
extern int strrpos (const char *s, char c);
extern int strspn (char *s, char *set);
extern int strcspn (char *s, char *set);
extern char *strpbrk (char *s, char *set);
extern char *strrpbrk (char *s, char *set);
extern char memcmp (void *s1, void *s2, int n);
extern void *memcpy (void *s1, void *s2, int n);
extern void *memchr (void *s, char val, int n);
extern void *memccpy (void *s1, void *s2, char val, int n);
extern void *memmove (void *s1, void *s2, int n);
extern void *memset (void *s, char val, int n);
#endif
#pragma RESTORE
