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Showing posts from February, 2014

Fixing "MySQL server has gone away" Errors in C

I ran across an old question on Stack Overflow the other day in which a user was having issues maintaining his connection to MySQL from C. I left a brief answer there for anyone else who might stumble across the same problem in the future, but I felt it was worth expanding on a bit more.The error "MySQL server has gone away" means the client's connection to the MySQL server was lost. This could be because of many reasons; perhaps MySQL isn't running, perhaps there's network problems, or perhaps there was no activity after a certain amount of time and the server closed the connection. Detailed information on the error is available in the MySQL documentation.It's possible for the client to attempt to re-connect to the server when it's "gone away" although it won't try to by default. To enable the reconnecting behavior, you need to set the MYSQL_OPT_RECONNECT option to 1 using the mysql_options() function. It should be set after mysql_init() is…

Generating C Code and Compiling from STDIN

Lately I've been exploring some syslog configurations and needed to generate some log messages to verify they were routed correctly. Of course doing so programmatically would provide an easy and repeatable method to generate a batch of fresh log messages whenever I needed, but because of the number of facilities and priorities defined by the syslog protocol, it made sense to write a code generator to iterate the different permutations.The following Lua script generates boilerplate C code for each of the 64 messages needed to test LOG_LOCAL 0-7 with all priorities. I chose generating the code in this manner over writing a nested facilities/priorities loop directly in C so I could easily include a textual representation of the facility and priority constants in the log message (this seemed like a cleaner solution to me than having to maintain a mapping of constants to char* strings as well). And why Lua? Well, it seemed a better idea than M4. :)#! /usr/bin/env lua local facilities …