C/C++ Doc

memccpy

void *memccpy(void * restrict dest, const void * restrict src, int c, size_t count);

dest  -    pointer to the object to copy to
src      -    pointer to the object to copy from
c      -    terminating character, converted to unsigned char at first
count -    number of characters to copy

这里容易出现理解偏差的是参数 c，“terminating character, converted to unsigned char at first” 也就是参数会转化为unsigned char 也就是需要传入的是单个字符，当检测到传入的src 中字符与”c”匹配时，停止copy，退出.

参考资料：

https://en.cppreference.com/w/c/string/byte/memccpy