Strcat () & strcpy () works even if there is not enough memory

When implementing infix on postfix algorithms and vice versa

I found,

char * str = (char*) malloc(1);
strcpy(str,str2);

this works even if it str2contains more than 1 character (20 characters or more).

I had no warnings or errors at runtime.

How is this possible?

Note:

I also did not receive garbage.

I always get the required result regardless str2.