C语言库函数实现

移动开发 2023-10-02 18:19:36 阅读次数: 0

C语言库函数实现

strcpy

#include<stdio.h>
#include<assert.h>

unsigned char* myStrcpy(unsigned char *dest,unsigned char *src)
{
     assert(dest!=NULL&&src!=NULL);
    
     unsigned char *bak=dest;

     while(*src)
     {
          *dest++=*src++;
     }
     *dest='\0';

     return bak;
} 

unsigned char* myStrcpy2(unsigned char *dest,unsigned char *src)
{
     assert(dest!=NULL&&src!=NULL);
    
     unsigned char *bak=dest;

     while((*dest++=*src++));
     *dest='\0';

     return bak;
}


unsigned char* myStrcpy3(unsigned char *dest,unsigned char *src)
{
     assert(dest!=NULL&&src!=NULL);
    
     unsigned char *bak=dest;

     while(*src)
     {
        *dest=*src;
         dest++;
         src++;        
     }
     *dest='\0';

     return bak;
}

int main()
{
   unsigned char str[128]={'\0'};
   unsigned char *p="xiewenhui";
   myStrcpy3(str,p);
   puts(str);

   return 0;
}

strncpy

#include<stdio.h>
#include<assert.h>

unsigned char* myStrncpy(unsigned char *dest,unsigned char *src,int count)
{
     assert(dest!=NULL&&src!=NULL);

     char *bak=dest;
     
     while(*src&&count>0)
     {
         *dest++=*src++;
         count--;
     }

     if(count>0)
     {
         while(count>0)
         {
             count--;
             *dest++='\0';
         }

         return dest;
     }

     *dest='\0';

     return bak;
}

int main()
{
    unsigned char str[128]={'\0'};
    unsigned char *p="xiewenhui";

    myStrncpy(str,p,15);
    puts(str);

    return 0;
}

strcat

#include<stdio.h>
#include<assert.h>
#include<string.h>

unsigned char* myStrcat(unsigned char *dest,unsigned char *src)
{
     assert(dest!=NULL&&src!=NULL);
     unsigned char *bak=dest;
    
     while(*dest)
     {
        dest++;
     }

     while(*src)
     {
        *dest++=*src++;
     }

     *dest='\0';

     return bak; 
}

unsigned char* myStrcat2(unsigned char *dest,unsigned char *src)
{
     assert(dest!=NULL&&src!=NULL);
     unsigned char *bak=dest;
    
     while(*dest)
     {
        dest++;
     }

     while((*dest++=*src++));
     *dest='\0';

     return bak; 
}

unsigned char* myStrcat3(unsigned char *dest,unsigned char *src)
{
     assert(dest!=NULL&&src!=NULL);
     
     unsigned char* bak=dest;
     strcpy(dest+strlen(dest),src);

     return bak;  
}

unsigned char* myStrcat4(unsigned char *dest,unsigned char *src)
{
     assert(dest!=NULL&&src!=NULL);

     unsigned char *bak=dest;

     for(;*dest!='\0';dest++);
     while((*dest++=*src++));

     return bak;
}

int main()
{
    unsigned char str[128]="xiewenhui";
    unsigned char *p="handsome";

    myStrcat4(str,p);
    puts(str);

    return 0;
}

strncat

#include<stdio.h>
#include<assert.h>

unsigned char* myStrncat(unsigned char *dest,unsigned char *src,int count)
{
     assert(dest!=NULL&&src!=NULL);
     
     unsigned  char *bak=dest;

     while(*dest)
     { 
        dest++;
     }

     while(*src&&count>0)
     {
        *dest++=*src++;
        count--;
     }
     
     if(count>0)
     {
        while(count>0)
        {
            count--;
            *dest++='\0';
        }

        return  dest;
     }

     *dest='\0';

     return  bak;
}


int main()
{
    unsigned char str[128]="xiewenhui";
    unsigned char *p="handsome";
    
    myStrncat(str,p,15);
    puts(str);

    return 0;
}

strcmp

#include<stdio.h>
#include<assert.h>

int myStrcmp(const unsigned char *str1,const unsigned char *str2)
{
 
     assert(str1!=NULL&&str2!=NULL);

     int ret=0;

     while(*str1&&str2&&(*str1==*str2))
     {
             str1++;
             str2++;
     }

     ret=str1-str2;
     if(ret>0)
     {
         return 1;
     }

     if(ret<0)
     {
         return -1;
     }

     return ret;
}

int main()
{
    int ret=0;

    unsigned char *str1="abcd";
    unsigned char *str2="bbcd";

    ret=myStrcmp(str1,str2);
    if(ret==1)
    {
      printf("第一个字符串大于第二个字符串\n");
    }
    else if(ret==-1)
    {
       printf("第一个字符串小于第二个字符串\n");
    }
    else
    {
        printf("两个字符串相等\n");
    }
     
    return 0;
}

strncmp

#include<stdio.h>
#include<assert.h>

int myStrncmp(const unsigned char* str1,const unsigned char* str2,int count)
{
    assert(str1!=NULL&&str2!=NULL);
    
    if(!count)
    {
       return 0;
    }

    while(*str1&&*str2&&(*str1==*str2)&&count--)
    {
         str1++;
         str2++;
    }
    
    return *str1-*str2;
}

int main()
{
    int ret=0;

    unsigned char *str1="abcd";
    unsigned char *str2="bbcd"; 

    ret=myStrncmp(str1,str2,4);
    printf("ret=%d\n",ret);

    return 0;
}

strlen

#include<stdio.h>

int myStrlen(unsigned char *str)
{
     int len=0;

     while(*str++)
     {
         len++;
     }

     return len;
}

int main()
{
    int len=0;
    unsigned char *p="xiewenhui";
    len=myStrlen(p);
    printf("len=%d\n",len);
}

strtok

#include<stdio.h>
//#include<string.h>
#include<assert.h>

char* myStrtok(char* p1, const char* p2)
{
	assert(p2);
	static char* pc = NULL;
	char* ret = NULL;
	char* p3 = (char*)p2;
	if (p1 == NULL && !*pc)
		return NULL;
	if (p1 != NULL)
		pc = p1;
	while (*pc && *p2)//去掉前面要被剪掉的
		if (*p2 == *pc)
		{
			pc++;
			p2 = p3;
		}
		else
			p2++;
	ret = pc;//初始化
	p2 = p3;
	while (*pc && *pc != *p2++)//确定标记点
		if (!*p2)
		{
			pc++;
			p2 = p3;
		}
	if (*pc)//判断是不是最后的点
		*pc++ = '\0';
	return ret;
}


int main()
{ 
    char str[128]="this is boy";
    char *p=NULL;
    
    printf("%s\n",p);
    p=myStrtok(str," ");
    while(p!=NULL)
    {
       printf("%s\n",p);
       p=myStrtok(NULL," ");
    }

    return 0;  
}

strstr

#include<stdio.h>
#include<assert.h>
#include<string.h>

char* myStrstr(char* str1,char* str2)
{
     assert(str1!=NULL&&str2!=NULL);

     char *bak1=str1;//保存字符串的首地址
     char *bak2=str2;//保存子串的首地址
     char *p=str1;

     while(*p)
     {
          bak1=p;;
          bak2=str2;
          while(*bak1&&*bak2&&*bak1==*bak2)
          {
               bak1++;
               bak2++;
          }
          if(*bak2=='\0')
          {
               return  p;
          }
          p++;
     }

     return NULL;
} 


int main()
{
    char str[] = "This is a simple string";
	char* pch;
	pch = myStrstr(str, "simple");
	if (pch != NULL)
		strncpy(pch, "sample", 6);
	puts(str);

    return 0;
}

memcpy

#include<stdio.h>
#include<assert.h>

void* myMemcpy(void *dest,void *src,int count)
{
     assert(dest!=NULL&&src!=NULL);

     void *bak=dest;
     
     while(count--)
     {
         *(char*)dest++=*(char*)src++;
     }

     return bak;
} 

int main()
{
    unsigned char str[128]={0};
    unsigned char *p="xiewenhui";
    myMemcpy(str,p,8);
    puts(str);
    return 0;
}

memset

#include<stdio.h>

void* myMemset(char *str,int n,int count)
{
     unsigned char *bak=str;

     while(count--)
     {
         *str++=n;  
     }
     
     return str;
}

int main()
{
    char str[128]="xiewenhui";
    myMemset(str,'\0',sizeof(str));
    printf("数据清空:%s",str);

    return 0;
}

memmove

void *memmove(void *dest, const void *src, size_t count)
{
    assert(dest != NULL || src != NULL)

    if (dst < src)
    {
        char *p = (char *)dest;
        char *q = (char *)src;
        while (count--)
        {
            *p++ = *q++;
        }
    }
    else
    {
        char *p = (char *)dest + count;
        char *q = (char *)src + count;
        while (count--)
        {
            *--p = *--q;
        }
    }

    return dest;
}

atoi

int isspace(int x)  
{  
    if (x == ' ' || x == '\t' || x == '\n' || x =='\f' || x =='\b' || x == '\r')  
        return 1;  
    else   
        return 0;  
}

int isdigit(int x)  
{
    if (x <= '9' && x >= '0')           
        return 1;   
    else   
        return 0;  
}

int my_atoi(const char *nptr)  
{  
    int c;              /*当前字符*/  
    int total;          /*总计字节数*/  
    int sign;           /*正数or负数*/     
  
    /*跳过开头的空格*/  
    while (isspace((unsigned char)*nptr))  
        ++nptr;  
  
    c = (unsigned char)*nptr++;  
    sign = c;           /*保存符号*/  
    if (c == '-' || c == '+')  
        c = (unsigned char)*nptr++;    /* skip sign */  
   
    total = 0;  
    while (isdigit(c)) 
    {  
        total = 10 * total + (c - '0');     /*求和*/  
        c = (unsigned char)*nptr++;    /*获取下一个字符*/  
    }
​
    if (sign == '-')  
        return -total;  
    else  
        return total;  
}

itoa

char* myitoa(int value, char* str, int radix) {
    static char dig[] =
        "0123456789"
        "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    int n = 0, neg = 0;
    unsigned int v;
    char* p, * q;
    char c;
    /* 负数：十进制直接在前面加负号，其它进制用补码 */
    if (radix == 10 && value < 0) {
        v = -value;
        neg = 1;
    }
    else
    {
        v = value;
    }
    /* 其它进制的负数转为unsigned int类型，即取了补码 */
    do {
        str[n++] = dig[v % radix];
        v /= radix;
    } while (v);
    if (neg)
        str[n++] = '-';
    str[n] = '\0';
    /* 字符串反转 */
    for (p = str, q = p + (n - 1); p < q; ++p, --q)
        c = *p, * p = *q, * q = c;
    return str;
}

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