strlen strcat strcpy strcmp 自己实现
2024-10-15 10:53:51
strlen strcat strcpy strcmp 自己实现
strlen
include <stdio.h>
#include <string.h>
#include <assert.h>
size_t my_strlen(const char* str){
assert(str != NULL);
const char *tmp = str;
size_t count = 0;
while(*tmp++ != '\0'){
count++;
}
return count;
}
size_t my_strlen1(const char* str){
assert(str != NULL);
if(*str == 0){
return 0;
}else{
return my_strlen1(str+1) + 1;
}
}
int main(){
char as[] = "hello C";
printf("%ld\n",strlen(as));
printf("%ld\n",my_strlen(as));
printf("%ld\n",my_strlen1(as));
}
strcat
#include <stdio.h>
#include <string.h>
#include <assert.h>
#include <malloc.h>
char* my_strcat(char* strd, const char* strs){
assert(strd != NULL && strs != NULL);
char *tmp = strd;
while(*tmp++ != 0){}
tmp--;
while(*strs != 0){
*(tmp++) = *strs++;
}
*tmp = '\0';
return strd;
}
int main(){
char s1[20] = "hello";
char s2[] = " C";
printf("strcat before s1 = %s\n", s1);
char *str = my_strcat(s1,s2);
printf("strcat after s1 = %s\n", s1);
printf("strcat after str = %s\n", str);
}
strcpy
#include <stdio.h>
#include <string.h>
#include <assert.h>
#include <malloc.h>
char* my_strcpy(char* strd, const char* strs){
assert(NULL != strd && NULL != strs);
char* tmp = strd;
while(*strs != '\0'){
*tmp++ = *strs++;
}
*tmp = '\0';
return strd;
}
int main(){
char s1[20] = "hello";
char s2[] = " wod";
printf("strcpy before s1 = [%s]\n", s1);
char *str = my_strcpy(s1,s2);
printf("strcpy after s1 = [%s]\n", s1);
printf("strcat after str = [%s]\n", str);
}
strcmp
#include <stdio.h>
#include <string.h>
#include <assert.h>
#include <malloc.h>
int my_strcmp(const char *s1, const char *s2){
assert(NULL != s1 && NULL != s2);
int res = 0;
while(*s1 != '\0' || *s2 != '\0'){
if(*s1 > *s2){
res = 1;
break;
}else if(*s1 < *s2){
res = -1;
break;
}else{
s1++;
s2++;
}
}
return res;
}
int main(){
char *s1 = "a1123";
char *s2 = "a1123";
int res = my_strcmp(s1, s2);
if(res == 0){
printf("s1 == s2\n");
}else if(res > 0){
printf("s1 > s2\n");
}else{
printf("s1 < s2\n");
}
}
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