string.h源码

strstr ( )/* -- C语言库函数源代码 - */ /* 得到s1中第一次包含s2字符串的位置指针。 */ #include <stdlib.h> char * my_strstr(const char *s1,const char *s2) { if (*s1 == 0) { if (*s2) return (char *) NULL; return (char *) s1; } while (*s1) { size_t i; i = 0; while (1) { if (s2[i] == 0) { return (char *) s1; } if (s2[i] != s1[i]) { break; } i++; } s1++; } return (char *) NULL; } int main() { char *str1 = "ammana_babi"; char *str2 = "babi"; char *p; if( (p = my_strstr(str1,str2)) == NULL) printf("Can't find the string /"%s/"!/n",str2); else printf("Find the string /"%s/"!/n",p); str1 = "abc"; str2 = "def"; if( (p = my_strstr(str1,str2)) == NULL) printf("Can't find the string /"%s/"!/n",str2); else printf("Find the string /"%s/"!/n",p); system("pause"); return 0; } strpbrk ( )/* -- C语言库函数源代码 - */ /* 得到s1中第一个且是s2中字符的位置指针。 */ #include <stdlib.h> char * my_strpbrk(const char *s1 ,const char *s2) { const char *c = s2; if (!*s1) return (char *) NULL; while (*s1) { for (c = s2; *c; c++) { if (*s1 == *c) break; } if (*c) break; s1++; } if (*c == '/0') s1 = NULL; return (char *) s1; } int main() { char *str1 = "ammana_babi"; char *str2 = "babi"; char *p; if( (p = my_strpbrk(str1,str2)) == NULL) printf("No same character!/n"); else printf("%c/n",*p); str1 = "abc"; str2 = "def"; if( (p = my_strpbrk(str1,str2)) == NULL) printf("No same character!/n"); else printf("%c/n",*p); system("pause"); return 0; } strcspn ( )/* -- C语言库函数源代码 - */ /* 得到s1中第一个且是s2中字符的字符位置。 */ int my_strcspn(const char *s1 ,const char *s2) { const char *s = s1; const char *p; while (*s1) { for (p = s2; *p; p++) { if (*s1 == *p) break; } if (*p) break; s1++; } return s1 - s; } int main() { char *str1 = "ammana_babi"; char *str2 = "babi"; int offset; if((offset = my_strcspn(str1,str2)) >= strlen(str1)) printf("Can't find the same character!/n"); else printf("%c/n",*(str1 + offset)); str1 = "abc"; str2 = "def"; if((offset = my_strcspn(str1,str2)) >= strlen(str1)) printf("Can't find the same character!/n"); else printf("%c/n",*(str1 + offset)); system("pause"); return 0; } strspn ( )/* -- C语言库函数源代码 - */ /* 得到s1中第一个且不是s2中任意字符的字符位置。 */ int my_strspn(const char *s1 ,const char *s2) { const char *s = s1; const char *p; while (*s1) { for (p = s2; *p; p++) { if (*s1 == *p) break; } if (*p == '/0') break; s1++; } return s1 - s; } int main() { char *str1 = "ammana_babi"; char *str2 = "babi"; int offset; if((offset = my_strspn(str1,str2)) >= strlen(str1)) printf("Can't find the different character!/n"); else printf("%c/n",*(str1 + offset)); str1 = "abc"; str2 = "abc"; if((offset = my_strspn(str1,str2)) >= strlen(str1)) printf("Can't find the different character!/n"); else printf("%c/n",*(str1 + offset)); system("pause"); return 0; } strrev ( )/* -- C语言库函数源代码 - */ /* Reverses the order of characters in the string. The terminating null character remains in place. 把字符串的所有字符的顺序颠倒过来（不包括空字符NULL）。 返回指向颠倒顺序后的字符串指针。 */ char * my_strrev(char *str) { char *right = str; char *left = str; char ch; while (*right) right++; right--; while (left < right) { ch = *left; *left++ = *right; *right-- = ch; } return(str); } /* 而我自己写的代码就略微显的有些啰里啰嗦，不简洁， 更不是很太爽快。这个问题是值得好好想一下的了。 下面就是我的垃圾代码 */ char * my_StrReverse(char * ch) { char tempch,* tch; int Len,i; tch = ch; Len = strlen(ch); for(i=0;i<Len/2;i++) { tempch = *tch; *tch = *(tch + Len - 2*i - 1); *(tch+Len-2*i-1) = tempch; tch++; } return ch; } int main() { char str[] ="ammana_babi"; puts(my_strrev(str)); puts(my_StrReverse(str)); system("pause"); return 0; } strnset ( )/* -- C语言库函数源代码 - */ /* Sets the first count characters of string the character value.If the length of string is less than count, the length of string is used in place of n. 把字符串的前count个字符设置为字符val。 */ char * my_strnset(char * str,int val,int count) { char *p = str; while (count-- && *p) *p++ = (char)val; return(p); } int main() { char str[] ="ammana_babi"; my_strnset(str,'*',strlen(str)-4); puts(str); system("pause"); return 0; } strset ( )/* -- C语言库函数源代码 - */ /* Sets all of characters in string (except the terminating '/0'character) equal to val. 把字符串的所有字符都设置为字符val。 */ char * my_strset(char *str,int val) { char *p = str; while (*str) *str++ = (char)val; return(p); } int main() { char str[] ="ammana_babi"; my_strset(str,'z'); puts(str); system("pause"); return 0; } strupr ( )/* -- C语言库函数源代码 - */ /* Force string to lower case。 将字符串转换为大写。只改变字符串中出现的小写字母，不改变其他字符。 */ char * my_strupr(char *str) { char *p = str; while (*p != '/0') { if(*p >= 'a' && *p <= 'z') *p -= 0x20; p++; } return str; } int main() { int i; char str1[]= "Ammana"; char str2[] = "baBi"; char str3[] = "AMMANA"; char str4[] = "aMmAn_BabI"; puts(my_strupr(str1)); puts(my_strupr(str2)); puts(my_strupr(str3)); puts(my_strupr(str4)); system("pause"); return 0; } strlwr ( )/* -- C语言库函数源代码 - */ /* Force string to lower case。 将字符串转换为小写。只改变字符串中出现的大写字母，不改变其他字符。 */ char * my_strlwr(char *str) { char *p = str; while (*p != '/0') { if(*p >= 'A' && *p <= 'Z') *p = (*p) + 0x20; p++; } return str; } int main() { int i; char str1[]= "Ammana"; char str2[] = "baBi"; char str3[] = "AMMANA"; char str4[] = "aMmAn_BabI"; puts(my_strlwr(str1)); puts(my_strlwr(str2)); puts(my_strlwr(str3)); puts(my_strlwr(str4)); system("pause"); return 0; } strdup ( )/* -- C语言库函数源代码 - */ /* Allocates enough storage via malloc() for a copy of the string, copies the string into the new memory, and returns a pointer to it. 复制字符串，返回指向被复制字符串的指针。所需空间由malloc()分配，且可以由free()释放。需要注意的是，在调用完这个函数后，一定要记得释放内存空间吆。 */ #include <stdlib.h> int my_strlen ( const char * str ) { const char *p = str; while( *p++ ) ; return( (int)(p - str - 1) ); } char * my_strcpy(char * dst, const char * src) { char * cp = dst; while( *cp++ = *src++ ) ; return( dst ); } char * my_strdup(const char *str) { char *p; if (!str) return(NULL); if (p = malloc(my_strlen(str) + 1)) return(my_strcpy(p,str)); return(NULL); } int main() { char *str = "ammana_babi"; char *p; p = my_strdup("ammana_babi"); puts(p); free(p); system("pause"); return 0; } strrchr ( )/* -- C语言库函数源代码 - */ /* Finds the last occurrence of ch in string. The terminating null character is used as part of the search. 查找在字符串中最后一次出现字符’ch’的位置。如果str中存在字符ch，返回出现ch的位置的指针；否则返回NULL。 */ #include <stdlib.h> char * my_strrchr(const char * str,int ch) { char *p = (char *)str; while (*str) str++; while (str-- != p && *str != (char)ch); if (*str == (char)ch) return( (char *)str ); return(NULL); } int main() { char *str = "ammana_babi"; char * p; char ch; ch = '9'; p = (char *)my_strrchr(str,ch); if(p == NULL) printf("Can't find the character %c !/n",ch); else printf("Find the character %c !/n",*p); ch = 'b'; p = (char *)my_strrchr(str,ch); if(p == NULL) printf("Can't find the character %c !/n",ch); else printf("Find the character %c !/n",*p); system("pause"); return 0; } strchr ( )/* -- C语言库函数源代码 - */ #include <stdlib.h> /* Searches a string for a given character, which may be the null character '/0'. 查找字符串string中首次出现字符ch的位置。如果string中存在字符ch，返回首次出现ch的位置的指针；否则返回NULL。 */ char * my_strchr(const char *str, int ch) { while (*str && *str != (char)ch) str++; if (*str == (char)ch) return((char *)str); return(NULL); } int main() { char *str = "ammana_babi"; char * p; char ch; ch = '9'; p = (char *)my_strchr(str,ch); if(p == NULL) printf("Can't find the character %c !/n",ch); else printf("Find the character %c !/n",*p); ch = 'b'; p = (char *)my_strchr(str,ch); if(p == NULL) printf("Can't find the character %c !/n",ch); else printf("Find the character %c !/n",*p); system("pause"); return 0; } memset ( )/* -- C语言库函数源代码 - */ /* Sets the first "count" bytes of the memory starting at "dst" to the character value "val". 把dst所指内存区域的前count个字节设置为val。返回指向dst的指针。 在实际应用中，我们有时候会用malloc函数来申请一些内存空间，这个内存空间有时候需要初始化，常用memset来进行初始化。 如： int *p; p = (int *)malloc( 0x400 * sizeof(int)); memset(p,0,0x400); */ void * my_memset(void *dst,int val,int count) { void *p = dst; while (count--) { *(char *)dst = (char)val; dst = (char *)dst + 1; } return p; } int main() { char str[] ="ammana_babi"; my_memset(str,'z',strlen(str)); puts(str); system("pause"); return 0; } memicmp ( )/* -- C语言库函数源代码 - */ /* memicmp perform a case-insensitive memory comparision. For differences,upper case letters are mapped to lower case.Thus, "abc_" < "ABCD" since "_" < "d". (与memcmp区别就是在比较的时候不区分大小写)比较内存区域buffer1和buffer2的前count个字节。当buffer1 < buffer2时，返回值 < 0；当buffer1 = buffer2时，返回值 0；当buffer1 > buffer2时，返回值 > 0。 */ int my_tolower(char ch) { if(ch >= 'A' && ch <= 'Z') return (ch + 0x20); return ch; } int my_memicmp(const void *buffer1,const void *buffer2,int count) { int f = 0; int l = 0; while (count--) { if ( (*(unsigned char *)buffer1 == *(unsigned char *)buffer2) || ((f = my_tolower( *(unsigned char *)buffer1 )) == (l = my_tolower( *(unsigned char *)buffer2 ))) ) { buffer1 = (char *)buffer1 + 1; buffer2 = (char *)buffer2 + 1; } else break; } return ( f - l ); } void Print(char * str1,char *str2,int t) { if(t > 0) printf("/n%s Upper Than %s/n",str1,str2); else if(t < 0) printf("/n%s Lower Than %s/n",str1,str2); else printf("/n%s Equal %s/n",str1,str2); } int main() { char *str1= "ammana"; char *str2 = "babi"; char *str3 = "AMMANA"; char *str4 = "bab_"; Print(str1,str2,my_memicmp(str1,str2,4)); Print(str3,str1,my_memicmp(str3,str1,4)); Print(str4,str2,my_memicmp(str4,str2,4)); system("pause"); return 0; }