C言語文字列ライブラリ関数の実現も筆記試験問題の常考問題であり、以下のコードは厳格にテストされず、簡単な実現である.
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C言語文字列ライブラリ関数の実現も筆記試験問題の常考問題であり、以下のコードは厳格にテストされず、簡単な実現である.
1.int strlen(const char *str) // 2.char *strcpy(char *to, const char *from)// 3.void * memset(void* buffer, int c, size_t count)// count c 4.char *strncpy(char *to, const char *from, size_t count)// from count， '\0'
5.char *strchr(char *str, int c) // s c
6.char *strcat(char *strDes, const char *strSrc) //
7.char *strncat(char *strDes, const char *strSrc, unsigned int count)
8.char *strstr(const char *strSrc, const char *str)//
9.char *strdup_(char *strSrc)////
10.void* memcpy(void* to, const void* from, size_t count)// 11.void* memmove(void* to, const void* from, size_t count)//
12.int strcmp(const char *s, const char *t)//
13.int stricmp(const char *dst, const char *src)//// （ ， ）14.
int strncmp(const char *s, const char *t, unsigned int count)// count
16.char * __cdecl strcat (char * dst,const char * src)18.size_t __cdecl strlen (const char * str)19.char * __cdecl strncpy (char * dest,const char * source,size_t count)//文字列の長さを求める
int strlen(const char *str)
{
assert(str != NULL);
int len = 0;
while (*str ++ != '\0')
++ len;
return len;
}
//
char *strcpy(char *to, const char *from)
{
assert((to != NULL) && (from != NULL));
char * result = to;
while( (*to++ = *from++) != '\0')
NULL;
return result;
}
// from count， '\0' char *strncpy(char *to, const char *from, size_t count)
{
assert((to != NULL) && (from != NULL));
char * result = to;
while(count--)
{
if(*from != '\0')
{
*to++ = *from++;
}
else
{
*to++ = '\0';
}
} return result;
}
//memset(): count void * memset(void* buffer, int c, size_t count)
{
assert(buffer != NULL);
char * p = (char *)buffer;
while(count--)
*p++ = (char)c;
return buffer;
}
// s c
char *strchr(char *str, int c)
{
assert(str != NULL);
for (; *str != (char)c; ++ str)
if (*str == '\0')
{
return NULL;
}
return str;
}
//
char *strcat(char *strDes, const char *strSrc)
{
assert((strDes != NULL) && (strSrc != NULL));
char *address = strDes;
while (*strDes != '\0')
++ strDes;
while ((*strDes ++ = *strSrc ++) != '\0')
NULL;
return address;
}
char *strncat(char *strDes, const char *strSrc, unsigned int count)
{
assert((strDes != NULL) && (strSrc != NULL));
char *address = strDes;
while (*strDes != '\0')
++ strDes;
while (count -- && *strSrc != '\0' )
*strDes ++ = *strSrc ++;
*strDes = '/0';
return address;
}
// char *strstr(const char *strSrc, const char *str)
{
assert(strSrc != NULL && str != NULL);
const char *s = strSrc;
const char *t = str;
for (; *strSrc != '\0'; ++ strSrc)
{
for (s = strSrc, t = str; *t != '\0' && *s == *t; ++s, ++t)
NULL;
if (*t == '\0')
return (char *) strSrc;
}
return NULL;
}
//
char *strdup_(char *strSrc)
{
if(strSrc!=NULL)
{
char *start=strSrc;
int len=0;
while(*strSrc++!='\0')
len++;
char *address=(char *)malloc(len+1);
assert(address != NULL);
while((*address++=*start++)!='\0');
return address-(len+1);
}
return NULL;
}メモリコピー関数:
//memcpy()
void* memcpy(void* to, const void* from, size_t count)
{
assert((to != NULL) && (from != NULL));
void * result = to;
char * pto = (char *)to;
char * pfrom = (char *)from;
assert(pto pfrom + count -1);
while(count--)
{ *pto++ = *pfrom++;
} return result;
}
//memmove(),
void* memmove(void* to, const void* from, size_t count)
{
assert((to != NULL) && (from != NULL));
void * result = to;
char * pto = (char *)to;
char * pfrom = (char *)from; //to from
if(pto pfrom + count -1)
{
while(count--)
{ *pto++ = *pfrom++;
}
} //to from ， move
else
{
pto = pto + count -1;
pfrom = pfrom + count -1;
while(count--)
{ *pto-- = *pfrom--;
}
} return result;
}文字列比較関数:
//
int strcmp(const char *s, const char *t)
{
assert(s != NULL && t != NULL);
while(*s && *t && *s == *t)
{
++ s;
++ t;
} return (*s - *t);
}
// （ ， ）int stricmp(const char *dst, const char *src)
{
assert(s != NULL && t != NULL);
int ch1, ch2;
while(*dst && *src)
{if((ch1 = (int)*dst) >= 'A' && (ch1 <= 'Z'))
ch1 += 0x20;
if((ch2 = (int)*src) >= 'A' && (ch2 <= 'Z'))
ch2 += 0x20;
if(ch1 == ch2)
{ ++ dst;
++ src;
}
else
break;
} return(ch1 - ch2);
}
int strncmp(const char *s, const char *t, unsigned int count)
{
assert((s != NULL) && (t != NULL));
while (*s && *t && *s == *t && count --)
{
++ s;
++ t;
}
return(*s - *t);
}c標準ライブラリ部分ソースコード
char * __cdecl strcat (char * dst,const char * src)
{
char * cp = dst;
while( *cp )
cp++; /* find end of dst */
while( *cp++ = *src++ ) ; /* Copy src to end of dst */
return( dst ); /* return dst */
}
int __cdecl strcmp (const char * src,const char * dst)
{
int ret = 0 ;
while( ! (ret = *(unsigned char *)src - *(unsigned char *)dst) && *dst)
++src, ++dst;
if ( ret 0 )
ret = 1 ;
return( ret );
}
size_t __cdecl strlen (const char * str)
{
const char *eos = str;
while( *eos++ ) ;
return( (int)(eos - str - 1) );
}
char * __cdecl strncat (char * front,const char * back,size_t count)
{
char *start = front;
while (*front++)
;
front--;
while (count--)
if (!(*front++ = *back++))
return(start);
*front = '\0';
return(start);
}
int __cdecl strncmp (const char * first,const char * last,size_t count)
{
if (!count)
return(0);
while (--count && *first && *first == *last)
{
first++;
last++;
}
return( *(unsigned char *)first - *(unsigned char *)last );
}
/* Copy SRC to DEST. */
char * strcpy (char * dest,const char* src)
{
reg_char c;
char *__unbounded s = (char *__unbounded) CHECK_BOUNDS_LOW (src);
const ptrdiff_t off = CHECK_BOUNDS_LOW (dest) - s - 1;
size_t n;
do
{
c = *s++;
s[off] = c;
}
while (c != '\0');
n = s - src;
(void) CHECK_BOUNDS_HIGH (src + n);
(void) CHECK_BOUNDS_HIGH (dest + n);
return dest;
}
char * __cdecl strncpy (char * dest,const char * source,size_t count)
{
char *start = dest;
while (count && (*dest++ = *source++)) /* copy string */
count--;
if (count) /* pad out with zeroes */
while (--count)
*dest++ = '\0';
return(start);
}