Become a Patron!

My Amazon wishlist can be found here.

Life Line

Contributing Advent 4: MongoDB driver variable names

A while ago I started reading Expert C Programming, a book on the intricacies of C, written almost 20 years ago (in 1994). I can very greatly recommend this book, even for seasoned C developers. Even although I know about most of the subjects addressed in the book, I picked up a few new things as well.

Anyway, the book made me look at my default compiler flags again. I tended not to use -Wall at all, but I've since then expanded my CFLAGS to -Wall -Wextra -Wdeclaration-after-statement -Wmissing-field-initializers -Wshadow -Wno-unused-parameter. When running with the new flags, the MongoDB driver for PHP started throwing (among others) the following warning during compilation:

/home/derick/dev/php/derickr-mongo-php-driver/bson.c:1069:12: warning: declaration of β€˜buffer’ shadows a global declaration [-Wshadow]
  char *buffer;

At first I found this odd, as I could not find the declaration at all, until I looked closer at the location where the compiler though I had the error:

In file included from /home/derick/dev/php/derickr-mongo-php-driver/bson.c:26:0:
/home/derick/dev/php/derickr-mongo-php-driver/php_mongo.h:301:3: warning: shadowed declaration is here [-Wshadow]
} buffer;

And this pointed me to the buffer struct:

typedef struct {
    char *start;
    char *pos;
    char *end;
} buffer;

This typedef declares buffer into the global scope and therefore the compiler rightfully warns us about this when trying to compile char *buffer; in a function. The fix was to add the prefix mongo_ so that the new name becomes mongo_buffer. The mongo_ prefix is what we use for all the other structs we define as well.


This article has a short URL available:


No comments yet

Add Comment


Will not be posted. Please leave empty instead of filling in garbage though!

Please follow the reStructured Text format. Do not use the comment form to report issues in software, use the relevant issue tracker. I will not answer them here.

All comments are moderated