bug687.cpp

1    #include <string.h>
2    struct deer_data
3        {
4        char *name; // deer name
5        double no2; // nitrous oxide emissions
6        double ch4; // methane emissions
7        double co2; // co2 emissions;
8        };
9    // the co2 equivalent of one reindeer's emissions
10   double co2( deer_data *p )
11       {
12       double total = p->co2;
13       if( strcmp( p->name, "Rudolph" ) == 0 )
14           total += 1.,   // energy surcharge?
15       total += p->no2 * 297.4;
16       total += p->ch4 * 23.2;
17       return total;
18       }

The UN commission on climate requested that Santa measure green house gas emissions from his reindeer. After gathering the data (phew, what a job) and running this program, he got strange results for non-Rudolph reindeer. Can you spot the problem?

bug687.cpp lint Output

--- Module:   bug687.cpp (C++)
                           _
    total += p->no2 * 297.4;
bug687.cpp(15) : Warning 687: Suspicious use of comma
    _
    }
bug687.cpp(18) : Info 818: Pointer parameter 'p' (line 10) could be declared as pointing to const

Reference Manual Explanation

687    Suspicious use of comma operator  -- A comma operator appeared unbraced and
       unparenthesized in a statement following an if, else, while or for clause.
       For example:

                 if( n > 0 ) n = 1,
                 n = 2;

       Thus the comma could be mistaken for a semi-colon and hence be the source of
       subtle bugs.

       If the statement is enclosed in curly braces or if the expression is enclosed
       in parentheses, the message is not issued.