[已解决]课后习题有疑问，望答疑。

风归来兮

没看懂这个语句是如何实现strncpy的作用的
while ((*target2++ = *target1++) != '\0')
;

最佳答案

月排行榜 / 总排行榜

ba21

2023-2-7 19:08:34

while ((*target2++ = *target1++) != '\0')
设：
*target2 == "ab\0"
*target1 == "ac\0"
1 -> *target1的值'a'赋值给*target2  ，得*target2='a' (target2处的值被赋值为'a'),    ('a')!='\0'?  随后target1，target2地址后移。
2 ->  *target1的值'c'赋值给*target2  ，得*target2='c' (target2处的值被赋值为'c')   ('c')!='\0'?  随后target1，target2地址后移。
3 ->  *target1的值'\0'赋值给*target2  ，得*target2='\0' (target2处的值被赋值为'\0')   ('\0')!='\0'?  随后target1，target2地址后移。
4 -> 注： 最后原target2处理的字符串会被替换为"ac\0"

跳转到最佳答案楼层

ba21

while ((*target2++ = *target1++) != '\0')
设：
*target2 == "ab\0"
*target1 == "ac\0"
1 -> *target1的值'a'赋值给*target2  ，得*target2='a' (target2处的值被赋值为'a'),    ('a')!='\0'?  随后target1，target2地址后移。
2 ->  *target1的值'c'赋值给*target2  ，得*target2='c' (target2处的值被赋值为'c')   ('c')!='\0'?  随后target1，target2地址后移。
3 ->  *target1的值'\0'赋值给*target2  ，得*target2='\0' (target2处的值被赋值为'\0')   ('\0')!='\0'?  随后target1，target2地址后移。
4 -> 注： 最后原target2处理的字符串会被替换为"ac\0"

两手空空儿

补充一下，优先级  * > ++  > =  
*target2++ = *target1 ++
等效为
*target2 = *target1;
target1++;
target2++;

人造人

两手空空儿 发表于 2023-2-8 10:46
补充一下，优先级  * > ++  > =  
*target2++ = *target1 ++
等效为

++ > *
https://fishc.com.cn/thread-67664-1-1.html

sh-5.1$ cat main.c
#include <stdio.h>

int main(void) {
    char s0[6] = "hello";
    char s1[6];
    char *target1 = s0;
    char *target2 = s1;
    //while((*target2++ = *target1++) != '\0');
    //while((*(target2++) = *(target1++)) != '\0');
    while(((*target2)++ = (*target1)++) != '\0');
    puts(s1);
    return 0;
}
sh-5.1$ gcc -g -Wall -o main main.c
main.c: In function ‘main’:
main.c:10:25: error: lvalue required as left operand of assignment
   10 |     while(((*target2)++ = (*target1)++) != '\0');
      |                         ^
sh-5.1$

两手空空儿

人造人 发表于 2023-2-8 20:13
++ > *
https://fishc.com.cn/thread-67664-1-1.html

好的，谢谢~~~~ 这些个小知识点总是记不清