C Language Implementation strlen () 4 Methods and strcat () 3 ways

#include <stdio.h> #include <assert.h> #if 0//default method 4//1 int strlen (const char* str) {int N;//const char *p = s Tr To test this sentence, this statement does not need to be, because my argument is a pointer, the parameter pointer changes to point to not affect the argument pointing to for (n = 0; *str! = ') '; n++) {str++;} return n;} #elif 0//Method 2 int strlen (const char* str) {int n = 0;for (; *str++; n++); return n;} #elif 0//Method 3 int strlen (const char* STR) {int n = 0;while (*str++) {n++;} return n;} #else//Method 4 int strlen (const char* str) {const char *p =str;while (*STR)//write while (*str++) not (because Str is added at return, 1 more), Must be written in the current code, str++; return str-p;} #endif #if 0char* strcat (char* str1, const char* str2) {assert ((str1!=null) && (str2!=null));//if ((str1==null) | | (Str2==null)) Throw "Invalide arguments!"; Char *p = str1;while (*p! = ') p++;while (*str2! = ') ' {*p = *str2;//error p++;str2++ occurred here;} *p = ' + '; return str1;} #elif 0char* strcat (char* str1,const char* str2) {assert ((str1!=null) && (str2!=null));//if ((str1==null) | | (Str2==null)) Throw "Invalide arguments!"; Char *p = str1;while (*p)//is written as a while (*p++) error for the reason that P++; while (*p++ = *str2++); return str1;}    #elsechar *strcat (Char *dst, char *src) {size_t Dst_len = strlen (DST);    int i;           for (i = 0; Src[i]! = ' + '; i++) Dst[dst_len + i] = src[i];    Dst[dst_len + i] = ' + '; return (DST);} #endifint Main (int argc, char **argv) {/* s best be large enough, otherwise overflow, here can be compiled and run, but do not do so */char s1[] = "AB";//Use char * = "AB", *s3 = "CDE";    Raw segment Error char s2[] = "CDE"; int len;strcat (S1,S2);    Len = strlen (S1); printf ("S1 =%s\n", s1);p rintf ("len =%d\n", len); return 0;}

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C Language Implementation strlen () 4 Methods and strcat () 3 ways