C compare pointers -

recently, wrote code compare pointers this:

if(p1+len < p2) 

however, staff said should write this:

if(p2-p1 > len) 

to safe. here,p1 , p2 char * pointers,len integer. have no idea that.is right?

edit1: of course,p1 , p2 pointer same memory object @ begging.

edit2：just 1 min ago,i found bogo of question in code(about 3k lines),because len big p1+len can't store in 4 bytes of pointer,so p1+len < p2 true.but shouldn't in fact,so think should compare pointers in some situation:

if(p2 < p1 || (uint32_t)p2-p1 > (uint32_t)len) 

in general, can safely compare pointers if they're both pointing parts of same memory object (or 1 position past end of object). when p1, p1 + len, , p2 conform rule, both of if-tests equivalent, needn't worry. on other hand, if p1 , p2 known conform rule, , p1 + len might far past end, if(p1-p2 > len) safe. (but can't imagine that's case you. assume p1 points beginning of memory-block, , p1 + len points position after end of it, right?)

what may have been thinking of integer arithmetic: if it's possible i1 + i2 overflow, know i3 - i1 not, i1 + i2 < i3 either wrap around (if they're unsigned integers) or trigger undefined behavior (if they're signed integers) or both (if system happens perform wraparound signed-integer overflow), whereas i3 - i1 > i2 not have problem.

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edited add: in comment, write "len value buff, may anything". in case, quite right, , p2 - p1 < len safer, since p1 + len may not valid.