Unreachable code in builtin-merge.c ?

4 messages, 3 authors, 2016-06-15 · open the first message on its own page

Unreachable code in builtin-merge.c ?

From: Zivkov, Sasa <hidden>
Date: 2016-06-15 22:47:36

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 ?

From: Mikael Magnusson <hidden>
Date: 2016-06-15 22:47:36

2009/10/23 Zivkov, Sasa [off-list ref]:
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 ?

From: Joshua Roys <hidden>
Date: 2016-06-15 22:47:36

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 ?

From: Zivkov, Sasa <hidden>
Date: 2016-06-15 22:47:36

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
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