胡图图想学c语言之字符串函数原型

#写函数原型

1.#include <stdio.h>
#include <assert.h>
size_t mystrlen(const char s){
assert(s!=NULL);
size_t len = 0;
for(;(s+len)!=’\0’;len++);
return len;
}
int main(){
char *p = “Hello world!\n”;
printf("%u\n",mystrlen§);
return 0;
}

2.#include <stdio.h>
#include <assert.h>
char *mystrcpy3(char *dest,const char *src){
assert(dest!=NULL && src!=NULL);
char *pdest = dest;
while((*dest++ = *src++) != ‘\0’);
return pdest;
}
int main(){
char s1[] = “Hello world”;
char s2[40] = “thanks how old are you”;
printf("%s\n",mystrcpy3(s2,s1));
printf("%s\n",s2);
return 0;
}

3.#include <stdio.h>
#include <assert.h>
char *mystrncpy2(char *dest,const char *src,size_t n){
assert(dest!=NULL && src!=NULL);
char *pdest = dest;
while(n-- > 0 && (*dest++ = *src++)!=’\0’);
return pdest;
}
int main(){
char str1[10] = “Hello xxx”;
char str2[10] = “world”;
mystrncpy2(str1,str2,6);
printf("%s\n",str1);
return 0;
}

4.#include <stdio.h>
#include <assert.h>
char *mystrcat1(char *dest,const char *src){
assert(dest!=NULL && src!=NULL);
char *pdest = dest;
while(*dest!=’\0’){
++dest;
}
while((*dest++ = *src++) != ‘\0’);
return pdest;
}
int main(){
char str1[100] = “Hello “;
char str2[100] = “world!”;
printf(”%s\n”,mystrcat1(str1,str2));
return 0;
}

5.#include <stdio.h>
#include <assert.h>
char *mystrncat2(char *dest,const char *src,size_t n){
assert(dest!=NULL && src!=NULL);
char *pdest = dest;
while(*dest != ‘\0’){
++dest;
}
while(n–>0 && ((*dest++)=(*src++))!=’\0’);
*dest = ‘\0’;
return pdest;
}
int main(){
char str1[100] = “Hello “;
char str2[100] = “world ! hello python”;
printf(”%s\n”,mystrncat2(str1,str2,10));
return 0;
}

6.#include <stdio.h>
#include <assert.h>
int mystrcmp(const char *s1,const char *s2){
assert(s1!=NULL && s2!=NULL);
while(*s1!=’\0’ && *s2 !=’\0’ && *s1 == *s2){
++s1;
++s2;
}
return *s1-*s2;
}
int main(){
printf("%d\n",mystrcmp(“Hello”,“Hello”));
printf("%d\n",mystrcmp(“hello”,“helloadasf”));
return 0;
}

7.#include <stdio.h>
#include <assert.h>
int mystrncmp(const char *s1,const char *s2,size_t n){
assert(s1!=NULL && s2!=NULL);
//剩下最后一个字符 直接比较 就不需要循环了
while(n–>1 && *s1!=’\0’&&*s2!=’\0’&&*s1==*s2){
s1++;
s2++;
}
return *s1-*s2;
}
int main(){
char str1[100] = “admin”;
char str2[100] = “admin123”;
printf("%d\n",mystrncmp(str1,str2,4))；
return 0;
}

8.#include <stdio.h>
#include <assert.h>

void *mymemcpy(void *dest,const void *src,size_t n){
assert(dest!=NULL && src!=NULL);
char *pdest = dest;
const char *psrc = src;
//while(n–>0 && *pdest++ = *psrc++);
while(n > 0){
*pdest++ = *psrc++;
–n;
}
return dest;
}
int main(){
double arr[] = {1,3.11,5.77,3.678,2.996};
double brr[5] = {};
mymemcpy(brr,arr,sizeof(arr));
int i = 0;
for(i=0;i<5;i++){
printf("%g “,brr[i]);
}
printf(”\n");
return 0;
}