c语言str_cpy和strn_cpy实现

最新推荐文章于 2023-10-26 19:32:16 发布

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本文介绍了一个C语言实现的字符串复制函数my_strcpy()和一个字符串截取函数my_strncpy()。my_strcpy()函数用于完全复制一个字符串到另一个位置，而my_strncpy()函数则用于复制指定数量的字符。文章还详细解释了这两个函数的工作原理。

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#include<stdio.h>
#include<assert.h>
char* my_strcpy(char *dest,const char* source){
	assert(dest!=NULL||source!=NULL);
	//store the address start of the dest string
	char* res=dest;
	while((*dest++=*source++)!='\0');
	return res;
}
int main(){
	char src[10]="qwertyuio";
	char dest[13];
	printf("%s",my_strcpy(dest,src));
	return 0;
}

char * strncpy ( char * destination, const char * source, size_t num );

Copy characters from string

Copies the first num characters of source to destination. If the end of the source C string (which is signaled by a null-character) is found before num characters have been copied, destination is padded with zeros until a total of num characters have been written to it.

No null-character is implicitly appended at the end of destination if source is longer than num. Thus, in this case, destination shall not be considered a null terminated C string (reading it as such would overflow).英文描述引用自 http://www.cplusplus.com/reference/cstring/strncpy/
从source字符串中拷贝num个字符到目标字符窜。如果在拷贝完num个字符之前源字符串的末尾(即'\0'空字符)就遇到了(src字符串长度比num小)，那么目标字符串将用0填充直到填满num个字符
如果源字符串比num长，那么非空字符'\0'不会附加到目标字符串。这种情形下，目标字符串不应该被认为是以空字符结束的字符串

#include<stdio.h>
char *my_strncpy(char * dest,const char * source,size_t num){
	char *res=dest;
	while(num--&&(*dest++=*source++)!='\0');
	while(num--)
		*dest++='\0';
	return res;
}

int main(){
	char src[10]="qwertyuio";
	char dest[13];
	printf("%s",my_strncpy(dest,src,12));
	return 0;
}