Implementation of string library functions

// String-series library functions: string = character array + '\ 0 ';
1 char * strcpy1 (char * strDest, const char * strSrc );
2 char * strncpy1 (char * strdest, const char * strsrc, int n );
3 int strcmp1 (const char * str1, const char * str2 );
4 int strlen1 (const char * str); // you can also use recursive thinking.
5 char * strstr1 (const char * str1, const char * str2 );
6 char * strcat1 (char * strDest, const char * strSrc );
7 void * memcpy1 (void * pvTo, const void * pvFrom, size_t size); // copy the memory

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1 char * strcpy1 (char * strDest, const char * strSrc );

Char * strcpy1 (char * strDest, const char * strSrc) {assert (strSrc! = NULL & strDest! = NULL); char * str = strDest; // while (str! = '\ 0') while (str! = NULL) The same mistake !!! While (* strSrc! = '\ 0') {* str ++ = * strSrc ++;} * str =' \ 0 '; // end with the string ending mark cout <strDest <endl; return strDest ;}

2 char * strncpy1 (char * strdest, const char * strsrc, int n)

Char * strncpy1 (char * strdest, const char * strsrc, int n) {assert (strdest! = NULL & strsrc! = NULL); char * str = strdest; int num = 0; while (* strsrc! = '\ 0' & num <n) {* str ++ = * strsrc ++; num ++;} if (num = n) {* str = '\ 0'; cout <"Copied successfully:" <strdest <endl; return strdest ;}cout <"Copied failed !!! "<Endl; return NULL ;}

3 int strcmp1 (const char * str1, const char * str2)

// Negative: Compare the value of each character. Positive values return 1. equal values return 0. Negative values return-1. int strcmp1 (const char * str1, const char * str2) {assert (str1! = NULL & str2! = NULL); int res = 0; // while (* s1 = * s2) {} res = * s1-* s2; while (! (Res = (unsigned char *) * str1-(unsigned char *) * str2) & (* str2) {str1 ++; str2 ++ ;} if (res> 0) {cout <1 <endl; return 1;} else if (res <0) {cout <-1 <endl; return-1 ;}cout <0 <endl; return 0 ;}

4 int strlen1 (const char * str)

Int strlen1 (const char * str) {assert (str! = NULL); int num = 0; const char * strtmp = str; // char * strtmp = str; error while (* strtmp! = '\ 0') {num ++; strtmp ++;} cout <"The number is" <num <endl; return num ;}

5 char * strstr1 (const char * str1, const char * str2)

Char * strstr1 (const char * str1, const char * str2) {assert (str1! = NULL & str2! = NULL); // const char * p = str1, * p2 = str2; char * p = (char *) str1, * p2 = (char *) str2; char * tmp = NULL; // tmp starts from the first matched character. While (* p! = '\ 0') {if (* p = * p2) {tmp = p; while (* tmp = * p2 & * p2! = '\ 0') {tmp ++; p2 ++;} if (* p2 =' \ 0') {cout <"match: "<p <endl; return p ;}} p ++ ;}cout <" failed to match! "<Endl; return NULL ;}

6 char * strcat1 (char * strDest, const char * strSrc)

// 1. Find the last position of strDest. 2. Create a one-to-one copy of the connection. Char * strcat1 (char * strDest, const char * strSrc) {/* assert (strDest! = NULL & strSrc! = NULL); int lenDest, lenSrc; lenDest = strlen (strDest); lenstrlen (strSrc); for (int I = 0; I <lenSrc; I ++) {strDest [lenDest + I] = strSrc [I];} strDest [lenDest + lenSrc] = '\ 0'; cout <strDest <endl; return strDest; * // Method 2: assert (strDest! = NULL & strSrc! = NULL); char * strP = strDest; while (* strP! = '\ 0') {strP ++;} // copy from the last position. While (* strSrc! = '\ 0') {* strP ++ = * strSrc ++;} * strP =' \ 0'; cout <strDest <endl; return strDest ;}

7 void * memcpy1 (void * pvTo, const void * pvFrom, size_t size); // copy the memory

Note: An error occurred during compilation !!

/// Memory copy can copy any data type --- convert to (byte *) // void * memcpy1 (void * pvTo, const void * pvFrom, size_t size) // {// assert (pvTo! = NULL & pvFrom! = NULL); // byte * memTo = (byte *) pvTo; // byte * memFrom = (byte *) pvFrom; // while (size> 0) // {// * memTo ++ = * memFrom ++; // size --; //} // return pvTo ;//}

Test code:

Char str1 [100], str2 [] = "nihao haha"; // strcpy1 (str1, str2); strncpy1 (str1, str2, 8 ); /* char * s1 = "Hello, world! "; Char * s2 =" Hello, World! "; Strcmp1 (s1, s2); * // strlen1 (str2); // outside the function, it can be: len = sizeof (str)/sizeof (char ); /* char * s1 = "Hello, world! "; Char * s2 =" world "; str1 (s1, s2); */char string1 [50] =" Thanks, thank you. "; char * s =" you are welcome. "; strcat1 (string1, s );