注意：最好的代码格式时候，我们还可以使用断言在函数的开始处检查参数的有效性。
strlen、strcpy、strcat、strcmp
int stringlen(const char *s){ int i = 0; assert(s != NULL); while (s[i]) { i++; } return i;} char *stringcpy(char *s1, const char *s2){ char *p = s1; assert((NULL != s1) && (NULL != s2)); while((*s1++ = *s2++) != '\0'); return p;} char *stringcat(char *s1, const char *s2){ char *p = s1; assert((NULL != s1) && (NULL != s2)); while(*s1) { s1++; } while(*s1++ = *s2++); return p;} int stringcmp(char *s1,char *s2){ assert((NULL != s1) && (NULL != s2)); while((*s1 == *s2)&& *s1) { s1++; s2++; } return (*s1 -*s2);} strchr、strrchr
char *stringchr(const char *s, char c){ assert(NULL != s); while(*s) { if(*s == c) { return s; } s++; } return NULL;} char *stringrchr(const char *s,char c){ char *p = NULL; while(*s) { if(*s == c) { p = s; } s++; } return p;} char *myitoa(int num,char *s){ int I = 0; while(num){ s[i++] = num%10 +’0’; num /= 10; } S[i] = 0; Reverse(s); Return s;} countchar
int countchar(const char *s,char c){ int num = 0; assert(NULL != s); while(*s) { if(*s == c) { num++; } s++; } return num;} max、secondmax
int max(int arr[],int n){ int i = 0; int max = arr[0]; for(i=1; i int find_secondmax(int arr[], int n){ int I; int max = arr[o]; int sec = arr[1]; if(arr[0] max){ Sec = max; Max = arr[i]; } If((arr[i] <=max) && (arr[i] >second)) Sec = arr[i]; } Return sec;} reverse
char *reverse(char *s);char *reverse(char *s){ //interative Inttemp, I, j = strlen(s)-1; For(I = 0;i<=j; j--, i++){ Temp = s[i]; S[i] = s[j]; S[j] = temp; } Return s;} Char *reverse(char *s){ //recursive Int I = 0; Char c; Int n = strlen(s); If(n == 1) Return; C = s[n -1]; For(i=n-1;i>0;i--) S[i] = s[i-1]; S[0] = c; Reverse(s++);}char *myitobin(int num,char *s){ int I = 0; while(num){ s[i++] = num%2 +’0’; num /= 2; } S[i] = 0; Reverse(s); Return s; } iton、atoi、htoi
char *myiton(int num,char *s,int base){ int i = 0; if(base >=2 && base <=10) { while(num) { s[i ++] = num % base + '0'; num /= base; } } else { if(base >= 11 && base <= 16) { if(num %base >= 10) { s[I ++] = num % base - 10 + 'a'; } else { s[i++] = num % base + '0'; } } else { fprintf(stderr, "base if error"); return NULL; } } s[i] = 0; reverse(s); return s;} int myatoi(char *s){ int n = 0; while(*s >= '0' && *s <= '9') { n = n*10 +(*s –'0'); s ++; } return n;} int myhtoi(char *s){ int n = 0; if((s[0] == ‘0’)&&((s[1] == ‘x’)||(*s == ‘X’))) { s = s +2; } while(*s) { if(*s >= '0' && *s <= '9') { n = n*16 +(*s –'0'); } else if(*s >= 'a' && *s <= 'f') { n = n*16 +(*s –'a')+10; } else if(*s >= 'A' && *s <= 'F') { n = n*16 +(*s –'A') + 10; } else { break; } s++; } return n;} strncmp
int stringncmp(char *s1, char *s2, int n){ while((*s1 == *s2) && (*s1) && (--n)) { s1++; s2++; } return (*s1 -*s2);} strstr、strrtr
char *strstr(char *s1, char *s2){ int len = strlen(s2); while(*s1) { if(!strncmp(s1,s2,len)) { return s1; } s1++; } return NULL;} char *strrstr(char *s1,char *s2){ int len = strlen(s2); char *p = NULL; while(*s1) { if(!strncmp(s1,s2,len)) { p = s1; } s1++; } return p;} squeeze、squeezestr
void squeeze(char *s, char c){ int I = 0,j = 0; while(s[i]) { if(s[i] != c) { s[j++] = s[i]; } i++; } s[j] = 0;} void squeezestr(char *s1,char *s2){ int len = strlen(s2); char *p = s1; while (*s1) { if(!strncmp(s1,s2,len)) { s1 = s1+len; } else { *p++ = *s1 ++; } } *p = 0;} bitcount
int bitcount(unsigned long n){ int num = 0; while(n) { if(n &1) { num += 1; } n >>= 1; } return num;} even_parity
int even_parity(unsigned long value,int n){ int count = 0, i; for(I = 0; i >=1; } Return (count%2 ==0);} getbits、setbits
int getbits(unsigned long value, int p,int n){ unsigned long num = 0; num = value <<(31-p); num = num >>(32-n); return num;} int setbits(unsigned long *value, int p,int n, int x){ unsigned num1 = *value; unsigned num2 = *value; num1 = (num1 <<(p+1)) <<(p+1); num2 = (num2 >>(31-p+n))>>(31-p+n); x = (x <<(32-n))>>(31-p); *value = num1|num2|x; return *value;} invert
int invert(unsigned long *value,int p,int n){ unsigned long temp = ~0; temp = (temp <<(32-n))>>(31-p); *value ^= temp; return *value;} reversebits
int reversebits(unsigned long *value){ int I = 0,j = 31; for(; i<= j; i++,j--) { if(((*value >>j) &1) ^ ((*value >>i)&1)) { *value ^= (1 >>j)|(1>>i); } } return *value;} rightrot
int rightrot(unsigned long *value,int n){ unsigned long num1 = *value <<(32-n); unsigned long num2 = *value >>n; *value = num1|num2; return *value;} swap
void swap(int *x,int *y){ *x = *x +*y; *y = *x -*y; *x = *x -*y;} fac 、fib
int fac(int n) //implementd by iterative mothods.{ int res = 1; while(n >1) { res = res *n; n--; } return res;} int fib(int n) //too{ int a = 1; int b = 1; int c = 0; while(n >1) { n--; c= b; b= a; a= b+c; } return a;} printd
void printd(int n){ if(n / 10) { printd(n /10); } putchar(n % 10 + '0');} 大端
int is_bigendian(){ unsigned long test_num = 0x12345678; if(*((short *)&test_num) == 0x1234) { fprintf(stderr, “bigendian”); return 1; } else { fprintf(stderr, “littleendian”); } return 0;} big_to_little16
int big_to_little16(unsigned short *x){ *x = (*x <<8)|(*x >.8); return *x;} big_to_little32
int big_to_little32(unsigned long *x){ *x = (*x >>24)|(*x &0x00ff0000)>>8 |(*x&0x0000ff00)<<8 |(*x<<24); return *x;} strspn
int stringspn(char *str,char *group){ int count = 0; while(*str) { if(strchr(group, *str)) { count ++; } else { break; } str++; } return count;} strcspn
int stringcspn(char *str,char *group){ int count = 0; while(*str) { if(!strchr(group, *str)) { count++; } else { break; } str++; }} strpbk
char *stringpbk(char *str,char *group){ while(*str) { if(strchr(group, *str)) { return str; } str++; } return NULL;} memcpy
void *memcpy(void *dst, const void *src,int len){ char *p1 = (char *)dst; char *p2 = (char *)src; int i = 0; for(i=0; i memcmp
int *memcmp(const void *dst, const void *src,int len){ char *p1 = dst; char *p2 = src; int i = 0; for (i=0; i memchr
void *memchr(void *s,int ch,int len){ char *p = s; int i = 0; for(;i memset
void *memset(void *s,int ch,int len){ char *p= s1; int i = 0; assert(NULL != s); for(i=0; i strdup
char *stringdup(char *str){ char *p = malloc(strlen(str) +1); if(NULL == p) { perror("no memoty"); exit(1); } strcpy(p, str); return p;} getmemory
int getmemory(void **p, int size){ *p = malloc(size); if(NULL != *p) { return -1; } return 0;}