模拟实现strncpy ,strncat,strncmp

strncpy

//1.模拟实现strncpy
#include<stdio.h>
#include<stdlib.h>
#include<assert.h>
void strncpy(char*dest,const char* source,int size){
	assert(dest!=NULL);
	assert(source!=NULL);
	int i = 0;
	int count = size;
	while (*(source+i)!=0&&count){
		*(dest + i) = *(source + i);
		i++;
		count--;
	}
	*(dest + i) = 0;
}
int main(){
	char source[] = "asasaasasasasas";
	char* dest=(char*)malloc(sizeof(char)*1024);
	strncpy(dest,source,5);
	printf("%s",dest);
	system("pause");
	return 0;
}

strncat

//1.模拟实现strncpy
#include<stdio.h>
#include<stdlib.h>
#include<assert.h>
void Strncat(char* dest,const char* source,int size){
	assert(dest!=NULL);
	assert(source!=NULL);
	int i = 0;
	int j = 0;
	int count = size;
	while (*(dest+i)!=0){
		i++;
	}
	while (*(source+j)!=0&&count){
		*(dest + i + j) = *(source + j);
		++j;
		--count;
	}
	*(dest + i + j) = 0;
}
int main(){
	int size = 4;
	char*  source = "abcdef";
	char  dest[100] = "aaaaaa";
	Strncat(dest,source,size);
	printf("%s",dest);
	system("pause");
	return 0;
}

strncmp

#include<stdio.h>
#include<stdlib.h>
#include<assert.h>
int Strncmp(const char* a, const char* b, int size){
	assert(a!=NULL);
	assert(a!=NULL);
	int i = 0;
	int count = size;
	while ((*(a + i) != 0 || *(b + i) != 0) && count){
		if (*(a + i)>*(b + i)){
			return 1;
		}
		else if (*(a + i)<*(b + i)){
			return -1;

		}
		else{
			++i;
		}
		count--;
	}
	return 0;
}
int main(){
	int i = 0;
	int size = 2;
	char* str1 = "abaaa";
	char* str2 = "aaaaab";
	int h = Strncmp(str1, str2, size);
	if (h>0){
		printf("str1>str2");
	}
	else if (h<0){
		printf("str1<str2");
	}
	else{
		printf("str1==str2");
	}
	system("pause");
	return 0;
}