[ILUG] C string concat question ??

[Paul J Collins]

>>>>> "SP" == Smelly Pooh <plop at redbrick.dcu.ie> writes:

    SP> In reply to Dave Neary's flatulent wordings, 
    >> Dave Neary wrote:
    >> > strcat((msg=strdup(strvar1),
    >> > (msg=realloc(msg,strlen(msg)+strlen(strvar2)+1))==NULL?
    >> >  bad_stuff():msg),strvar2);
    >> 
    >> works :) I was only confusing myself with the whole "order of
    >> evaluation" red herring, since the first arg doesn't go near the second
    >> arg. But anyone who ever used this should be shot :)

    SP> If order of evaluation was right to left however then you will
    SP> be realloccing an unallocated msg, strlen() msg which could
    SP> lead to a seg fault if msg doesn't point somewhere valid and
    SP> generaly make things quite sucky

The comma operator is totally different to the comma that separates
arguments to a function.  Expressions are sequenced by the comma
operator and are executed from left-to-right, in order.  The strdup
will thus always evaluate before the realloc.  Nevertheless, it is
bad, nasty code that does not buy you anything except, perhaps, job
security.

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