[Bug libc/29313] New: MIN/MAX macros can cause double evaluation of arguments

["gkoumplias at gmail dot com" <sourceware-bugzilla@sourceware.org>]

https://sourceware.org/bugzilla/show_bug.cgi?id=29313

            Bug ID: 29313
           Summary: MIN/MAX macros can cause double evaluation of
                    arguments
           Product: glibc
           Version: 2.36
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: libc
          Assignee: unassigned at sourceware dot org
          Reporter: gkoumplias at gmail dot com
                CC: drepper.fsp at gmail dot com
  Target Milestone: ---

* MIN, MAX macros as defined in misc/sys/param.h
https://sourceware.org/git/?p=glibc.git;a=blob_plain;f=misc/sys/param.h;hb=HEAD
can cause the double evaluation of one of the passed in arguments.
Currently MAX is defined as:
#define MAX(a,b) (((a)>(b))?(a):(b))
This will evaluate the maximum argument twice.

* A test case to reproduce this would go like this:
int a = 1000;
int b = 10;
MAX(a++, b++) ;
// This will fail as a will be 1002 due to double evaluation by the MAX macro
EXPECT_EQ(a, 1001)

* solution
#define max(a,b) \
   ({ __typeof__ (a) _a = (a); \
       __typeof__ (b) _b = (b); \
     _a > _b ? _a : _b; })

* A discussion (and a solution) for the matter can be found here
https://stackoverflow.com/questions/3437404/min-and-max-in-c


Thanks

-- 
You are receiving this mail because:
You are on the CC list for the bug.