将会发生什么，我们将-1作为strncmp（）中第3个参数的值传递。 n个数字字节要比较的字节数？

Question

I have three questions,

1. What will happen we pass -1 as value for 3rd parameter in strncmp() ie. n number bytes of bytes to compare?
2. Why the output differs in ARM and PPC? ie. if which one correct?

3. If I use memcmp instead of strncmp, I m getting "inside else" output in both ARM and PPC. How and why?

    char str[10]; memset(str,'\\0',sizeof(str)); printf("str:%s ,len:%d\\n\\r",str,strlen(str)); if(strncmp(str,"Maximum",(strlen(str)-1)) == 0) { printf("inside if\\n\\r"); } else { printf("inside else\\n\\r"); } 

Output in ppc

str: ,len:0
inside else

Output in arm

str: ,len:0
inside if

Answer 1

What will happen we pass -1 as value for 3rd parameter in strncmp()

Assuming the 3rd parameter is defined a being of size_t and furthermore assuming size_t is defined as unsigned integer, passing in -1 will result in a "wrap-around" and the function will receiving the value of SIZE_MAX . On a 32bit system this probably would be 0xffffffff .