Red Hat Bugzilla – Bug 103061
hsearch_r needs better example code
Last modified: 2007-04-18 12:57:08 EDT
From Bugzilla Helper: User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.2.1) Gecko/20030225 Description of problem: I'm converting a perl program to C, and wanted to use some hash tables. I found the hcreate_r, hsearch_r, hdestroy_r functions in the man pages. There is an example on how to use the old (non-reentrant) versions of these functions, but when I tried to upgrade it to use the reentrant functions the test program died a horrible death, mysteriously. After much debugging, I found the problem and the solution. Version-Release number of selected component (if applicable): man-pages-1.53-3 How reproducible: Always Steps to Reproduce: 1. Cut-n-paste the example from the man page 2. Define a 'struct hsearch_data foo;' in main() 3. Convert the old functions to the new functions. 4. Compile and run. Actual Results: Crash with 'Segmentation fault' or 'Floating point error'. Expected Results: Should have run without an error. Additional info: It turns out that the example program doesn't check the return value of the hcreate call. If it fails to create the hash table, a divide-by-zero error will occur in the hsearch function. The other problem is that I didn't zero out the hsearch_data before calling hcreate_r, which causes hcreate_r to assume that a table was already created and so it refuses to clobber an existing hash table. I'm including an example for the new functions.
Created attachment 93928 [details] example program for inclusion in the man page This code shows a working example for hcreate_r/hsearch_r. It is almost identical to the hcreate/hsearch example, except that it clears a data structure before use, and it checks to see if the hash table was created.
h_search and Co. is not in the latest man-pages package