目錄

1.?void *mymemcpy(void *dest, const void* src, size_t n)；

2.void *memset(void *s, int c, size_t n);

3.?char* strcpy(char* dest,const char* src);

4.?char* mystrncpy(char* dest,char* src,size_t n);

5.char* strcat(char* dest,const char* src)

6.int strcmp(const char* s1,const char* s2)

7.size_t strlen(const char* s)

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1.?void *mymemcpy(void *dest, const void* src, size_t n)；

? ? ?內存拷貝函數，memcpy函數的功能是從源src所指的內存地址的起始位置開始拷貝n個字節到目標dest所指的內存地址的起始位置中

void* memcpy(void* dest,void* src,size_t n){assert(dest != NULL && src != NULL);if(src < dest && (char*)src + n > dest){char* pdst = (char*)dest+n-1;char* psrc = (char*)src+n-1;while(n--){*pdst-- = *psrc--;}}else{char* pdest = (char*)dest;char* psrc = (char*)src;while(n--){*pdest++ = *psrc++;}}return dest; }

2.void *memset(void *s, int c, size_t n);

void* memset(void* src,int c,size_t n){assert(src != NULL);char* psrc = (char*)src;while(n--){*psrc++ = (char)c;}return src;}

3.?char* strcpy(char* dest,const char* src);

char* strcpy(char* dest,const char* src){assert(dest != NULL && src != NULL);size_t n = strlen(src);if(src < dest && src + n > dest){char* pdst = dest + n;*pdst-- = '\0';src = src + n - 1;while(n--){*pdst-- = *src--;}}else{char* pdst = dest;while((*pdst++ = *src++) != 0);}return dest; }

4.?char* mystrncpy(char* dest,char* src,size_t n);

char* strncpy(char* dest,const char* src,size_t n){assert(dest != NULL && src != NULL);if(src < dest && src + n > dest){int m = strlen(src) < n ? strlen(src):n;char* pdst = dest+m;*pdst-- = '\0';src = src + m-1;while(m--){*pdst-- = *src--;}}else{char* pdst = dest;size_t i = 0;while(i++ < n && (*pdst++ = *src++) != '\0');if(*(pdst-1) != '\0') *pdst = '\0';}return dest; }

5.char* strcat(char* dest,const char* src)

char* strcat(char* dest,const char* src){assert(dest != NULL && src != NULL);char* pdst = dest;while(*pdst != '\0'){pdst++;}while((*pdst++ = *src++) != '\0');return dest; }

6.int strcmp(const char* s1,const char* s2)

int strcmp(const char* s1,const char* s2){assert(s1 != NULL && s2 != NULL);while(s1 && s2 && *s1 == *s2){s1++;s2++;}return *s1 - *s2; }

7.size_t strlen(const char* s)

size_t strlen(const char* src){assert(src != NULL);size_t ret = 0;while(*src++ != '\0'){ret++;}return ret; }

總結

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