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This article mainly shows you "how to simulate the implementation of str series library functions", the content is simple and easy to understand, clear organization, I hope to help you solve doubts, let Xiaobian lead you to study and learn "how to simulate the implementation of str series library functions" this article bar.

strlen #include size_t strlen( char *str );

Function: Returns the length of string str (i.e. the number of characters before the null terminator).

nonrecursive realization

size_t my_strlen(const char* src){ assert(src); size_t len = 0; while (*src++ != '\0') ++len; return len;}

recursive implementation

int my_strlen2(const char* strDest) //recursively find string length { assert(strDest); if ('\0' == *strDest) return 0; else return (1 + my_strlen(++strDest));}strcpy #include char *strcpy( char *to, const char *from );

Function: Copy characters from string from to string to, including null terminator. Return value is pointer to.

Regardless of memory overlap

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

Consider memory overlap

char *my_strcpy(char *dst,const char *src){ assert(dst && src); char *ret = dst; my_memcpy(dst,src,strlen(src)+1); return ret;}

where my_memcpy is implemented as follows:

void * my_memcpy(void *dst, const void *src, size_t count){ assert(dst && src); char* pdst = (char*)dst; char* psrc = (char*)src; int n = count; if (pdst > psrc && pdst

< (psrc + count)) //重叠 { for (size_t i = n - 1; i != -1; --i) pdst[i] = psrc[i]; } else { for (size_t i = 0; i < n; ++i) pdst[i] = psrc[i]; } return dst;} strncpy #include char *strncpy( char *to, const char *from, size_t count ); 功能：将字符串from 中至多count个字符复制到字符串to中。如果字符串from 的长度小于count，其余部分用'\0'填补。返回处理完成的字符串。 char* my_strncpy(char* dst, const char* src, size_t n) { assert(dst && str); char* pdst = dst; const char* psrc = src; while (n && (*pdst++ = *psrc ++) != '\0') { --n; } if (n) //如果n==0 则下面会死循环 { while (n--) { *pdst++ = '\0'; } } return dst;} strstr #include char *strstr( const char *str1, const char *str2 ); 功能：函数返回一个指针，它指向字符串str2 首次出现于字符串str1中的位置，如果没有找到，返回NULL。 char* my_strstr(const char* src, const char* sub) { assert(src && sub); int sublen = strlen(sub); char* srctmp = NULL; char* subtmp = NULL; while (strlen(src) >

= sublen) //strlen(src) is constantly updated and can end the loop early { srctmp = (char*)src; subtmp = (char*)sub; while (*srctmp == *subtmp) { if (*subtmp == '\0') return (char*)src; ++srctmp; ++subtmp; } if (*subtmp == '\0') return (char*)src; ++src; } return NULL;} strcat #include char *strcat( char *str1, const char *str2 );

Function: The function concatenates the string str2 to the end of str1 and returns the pointer str1.

char* my_strcat(char* dst, const char* str){ assert(dst && str); char* pdst = dst; while (*pdst != '\0')//Note that this cannot be *pdst++ != '\0' will add one more time! ++pdst; while (*str != '\0') *pdst++ = *str++; *pdst = '\0'; return dst;} strncat #include char *strncat( char *str1, const char *str2, size_t count );

Function: Concatenate at most count characters in the string from into the string to, appending a null terminator. Returns the processed string.

char* my_strncat(char *dst, const char *str, size_t n){ assert(dst && str); char* pdst = dst; while (*pdst != '\0') ++pdst; while (n && (*pdst = *str) != '\0') { --n; ++pdst; //better to do this, don't put it inside while ++str; } *pdst = '\0'; return dst;} strcmp #include int strcmp( const char *str1, const char *str2 );

Function: Compare string str1 and str2, the return value is as follows:

return value

explain

less than 0

str1 is less than str2

equal to 0

str1 is equal to str2

greater than 0

str1 is greater than str2

int my_strcmp(const char *str1, const char *str2){ assert(str1 && str2); const char* pstr1 = str1; const char* pstr2 = str2; while (*pstr1 && *pstr2 && (*pstr1 == *pstr2)) { ++pstr1; ++pstr2; } return *pstr1 - *pstr2;} strncmp #include int strncmp( const char *str1, const char *str2, size_t count );

Function: Compare strings str1 and str2 for up to count characters. The return values are as follows:

return value

explain

less than 0

str1 is less than str2

equal to 0

str1 is equal to str2

greater than 0

str1 is greater than str2

If the length of any string in the argument is less than count, the comparison ends when the first null terminator is reached.

int my_strncmp(const char *str1, const char *str2, size_t n){ assert(str1 && str2 && n > 0); const char* pstr1 = str1; const char* pstr2 = str2; while (--n && *pstr1 && *pstr2 && (*pstr1 == *pstr2)) { ++pstr1; ++pstr2; } return *pstr1 - *pstr2;} This is all the content of "How to simulate str series library functions", thank you for reading! I believe that everyone has a certain understanding, hope to share the content to help everyone, if you still want to learn more knowledge, welcome to pay attention to the industry information channel!

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