Dyntex.net Support Centre: MySQL Reference Manual p.623

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Table of Contents
1. General Information
2. MySQL Installation
3. Tutorial Introduction
4. Database Administration
5. MySQL Optimisation
6. MySQL Language Reference
7. MySQL Table Types
8. MySQL APIs
9. Extending MySQL

Chapter 9: Extending MySQL 623 memcpy(result, "result string", 13); *length = 13; The result buer that is passed to the calc function is 255 byte big. If your result ts in this, you don't have to worry about memory allocation for results. If your string function needs to return a string longer than 255 bytes, you must allocate the space for it with malloc() in your xxx_init() function or your xxx() function and free it in your xxx_deinit() function. You can store the allocated memory in the ptr slot in the UDF_INIT structure for reuse by future xxx() calls. See Section 9.2.2.1 [UDF calling], page 619. To indicate a return value of NULL in the main function, set is_null to 1: *is_null = 1; To indicate an error return in the main function, set the error parameter to 1: *error = 1; If xxx() sets *error to 1 for any row, the function value is NULL for the current row and for any subsequent rows processed by the statement in which XXX() was invoked. (xxx() will not even be called for subsequent rows.) Note: in MySQL versions prior to 3.22.10, you should set both *error and *is_null: *error = 1; *is_null = 1; 9.2.2.5 Compiling and Installing User-denable Functions Files implementing UDFs must be compiled and installed on the host where the server runs. This process is described below for the example UDF le `udf_example.cc' that is included in the MySQL source distribution. This le contains the following functions: metaphon() returns a metaphon string of the string argument. This is something like a soundex string, but it's more tuned for English. myfunc_double() returns the sum of the ASCII values of the characters in its argu- ments, divided by the sum of the length of its arguments. myfunc_int() returns the sum of the length of its arguments. sequence([const int]) returns an sequence starting from the given number or 1 if no number has been given. lookup() returns the IP number for a hostname. reverse_lookup() returns the hostname for an IP number. The function may be called with a string "xxx.xxx.xxx.xxx" or four numbers. A dynamically loadable le should be compiled as a sharable object le, using a command something like this: shell> gcc -shared -o udf_example.so myfunc.cc You can easily nd out the correct compiler options for your system by running this com- mand in the `sql' directory of your MySQL source tree:

MySQL Reference Manual

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