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hwdb: fix dangling 'else' ambuguity

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Imagine the following use of hwdb:

    if (condition_A)
        SD_HWDB_FOREACH_PROPERTY(hwdb, modalias, key, value)
            operation_A(key, value);
    else
        log_error("...");

This should work just fine, but but definitely does not what you would
expect. Due to how SD_HWDB_FOREACH_PROPERTY is defined, the dangling
'else' is linked to the hidden 'if' statement in the macro instead of the
outer 'if (condition_A)'. This is unexpected and really annoying to debug.

Fix this by never leaving un-finished if-statements in
SD_HWDB_FOREACH_PROPERTY(). We simply inverse the if() statement and
explicitly add an 'else'-branch. This way, the statement is closed and all
ambuguities are resolved.
This commit is contained in:
David Herrmann
2014-12-12 09:43:54 +01:00
parent 0b93157191
commit bff686e2a9
1 changed files with 3 additions and 2 deletions
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src/systemd/sd-hwdb.h
+3 -2
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@@ -39,8 +39,9 @@ int sd_hwdb_get(sd_hwdb *hwdb, const char *modalias, const char *key, const char
int sd_hwdb_seek(sd_hwdb *hwdb, const char *modalias);
int sd_hwdb_enumerate(sd_hwdb *hwdb, const char **key, const char **value);
/* the inverse condition avoids ambiguity of danling 'else' after the macro */
#define SD_HWDB_FOREACH_PROPERTY(hwdb, modalias, key, value) \
if (sd_hwdb_seek(hwdb, modalias) >= 0) \
while (sd_hwdb_enumerate(hwdb, &(key), &(value)) > 0)
if (sd_hwdb_seek(hwdb, modalias) < 0) { } \
else while (sd_hwdb_enumerate(hwdb, &(key), &(value)) > 0)
#endif