Unreachable code in builtin-merge.c ?

Unreachable code in builtin-merge.c ?

[Zivkov, Sasa]

In the try_merge_strategy function the expression in the following if statement seems to always evaluate to TRUE:

        if (!strcmp(strategy, "recursive") || !strcmp(strategy, "subtree")) {

If strategy is "recursive" then !strcmp(strategy, "subtree") evaluates to TRUE.
If strategy is "subtree" then !strcmp(strategy, "recursive") evaluates to TRUE.
If strategy is neither "recursive" nor "subtree" then any side of || evaluates to TRUE.

Looks like the code in the else block is unreachable?


Saša Živkov

Re: Unreachable code in builtin-merge.c ?

[Mikael Magnusson]

2009/10/23 Zivkov, Sasa <sasa.zivkov@sap.com>:
> In the try_merge_strategy function the expression in the following if statement seems to always evaluate to TRUE:
>
>        if (!strcmp(strategy, "recursive") || !strcmp(strategy, "subtree")) {
>
> If strategy is "recursive" then !strcmp(strategy, "subtree") evaluates to TRUE.
> If strategy is "subtree" then !strcmp(strategy, "recursive") evaluates to TRUE.
> If strategy is neither "recursive" nor "subtree" then any side of || evaluates to TRUE.
>
> Looks like the code in the else block is unreachable?

You seem to have forgotten that strcmp returns 0 when the strings
match. (It returns -1 or 1 when they don't, depending on their
alphabetical ordering).

-- 
Mikael Magnusson

Re: Unreachable code in builtin-merge.c ?

[Joshua Roys]

On 10/23/2009 11:03 AM, Zivkov, Sasa wrote:
> In the try_merge_strategy function the expression in the following if statement seems to always evaluate to TRUE:
>
>          if (!strcmp(strategy, "recursive") || !strcmp(strategy, "subtree")) {
>
> If strategy is "recursive" then !strcmp(strategy, "subtree") evaluates to TRUE.
> If strategy is "subtree" then !strcmp(strategy, "recursive") evaluates to TRUE.
> If strategy is neither "recursive" nor "subtree" then any side of || evaluates to TRUE.
>
> Looks like the code in the else block is unreachable?
>
>
> Saša Živkov
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Hello,

Not quite :)  The strcmp() function actually returns 0 when the strings 
match (I know, it looks weird "!strcmp" -> "not string compare?!"), so 
the "if" really means: "if strategy is equal to 'recursive' or 
'subtree', do the following..."

Hope to help,

Josh

RE: Unreachable code in builtin-merge.c ?

[Zivkov, Sasa]

> Not quite :)  The strcmp() function actually returns 0 when the strings
> match (I know, it looks weird "!strcmp" -> "not string compare?!"), so

Right! Now I remember it :-)

This is what happens when one looks at C code after some 10+ years of !C development ;-)

Saša Živkov