Retrieving Arguments

Parsing parameters is a very common operation and it may get a bit tedious. It would also be nice to have standardized error checking and error messages. Since PHP 4.1.0, there is a way to do just that by using the new parameter parsing API. It greatly simplifies the process of receiving parameteres, but it has a drawback in that it can't be used for functions that expect variable number of parameters. But since the vast majority of functions do not fall into those categories, this parsing API is recommended as the new standard way.

The prototype for parameter parsing function looks like this:

int zend_parse_parameters(int num_args TSRMLS_DC, char *type_spec, ...);

The first argument to this function is supposed to be the number of actual parameters passed to your function, so ZEND_NUM_ARGS() can be used for that. The second parameter should always be TSRMLS_CC macro. The third argument is a string that specifies the number and types of arguments your function is expecting, similar to how printf format string specifies the number and format of the output values it should operate on. And finally the rest of the arguments are pointers to variables which should receive the values from the parameters.

zend_parse_parameters() also performs type conversions whenever possible, so that you always receive the data in the format you asked for. Any type of scalar can be converted to another one, but conversions between complex types (arrays, objects, and resources) and scalar types are not allowed.

If the parameters could be obtained successfully and there were no errors during type conversion, the function will return SUCCESS, otherwise it will return FAILURE. The function will output informative error messages, if the number of received parameters does not match the requested number, or if type conversion could not be performed.

Here are some sample error messages:

Warning - ini_get_all() requires at most 1 parameter, 2 given Warning - wddx_deserialize() expects parameter 1 to be string, array given

Of course each error message is accompanied by the filename and line number on which it occurs.

Here is the full list of type specifiers:

• l - long

• d - double

• s - string (with possible null bytes) and its length

• b - boolean

• r - resource, stored in zval*

• a - array, stored in zval*

• o - object (of any class), stored in zval*

• O - object (of class specified by class entry), stored in zval*

• z - the actual zval*

• | - indicates that the remaining parameters are optional. The storage variables corresponding to these parameters should be initialized to default values by the extension, since they will not be touched by the parsing function if the parameters are not passed.

• / - the parsing function will call SEPARATE_ZVAL_IF_NOT_REF() on the parameter it follows, to provide a copy of the parameter, unless it's a reference.

• ! - the parameter it follows can be of specified type or NULL (only applies to a, o, O, r, and z). If NULL value is passed by the user, the storage pointer will be set to NULL.

The best way to illustrate the usage of this function is through examples:

/* Gets a long, a string and its length, and a zval. */ long l; char *s; int s_len; zval *param; if (zend_parse_parameters(ZEND_NUM_ARGS() TSRMLS_CC, "lsz", &l, &s, &s_len, &param) == FAILURE) { return; } /* Gets an object of class specified by my_ce, and an optional double. */ zval *obj; double d = 0.5; if (zend_parse_parameters(ZEND_NUM_ARGS() TSRMLS_CC, "O|d", &obj, my_ce, &d) == FAILURE) { return; } /* Gets an object or null, and an array. If null is passed for object, obj will be set to NULL. */ zval *obj; zval *arr; if (zend_parse_parameters(ZEND_NUM_ARGS() TSRMLS_CC, "O!a", &obj, &arr) == FAILURE) { return; } /* Gets a separated array. */ zval *arr; if (zend_parse_parameters(ZEND_NUM_ARGS() TSRMLS_CC, "a/", &arr) == FAILURE) { return; } /* Get only the first three parameters (useful for varargs functions). */ zval *z; zend_bool b; zval *r; if (zend_parse_parameters(3, "zbr!", &z, &b, &r) == FAILURE) { return; }

Note that in the last example we pass 3 for the number of received parameters, instead of ZEND_NUM_ARGS(). What this lets us do is receive the least number of parameters if our function expects a variable number of them. Of course, if you want to operate on the rest of the parameters, you will have to use zend_get_parameters_array_ex() to obtain them.

The parsing function has an extended version that allows for an additional flags argument that controls its actions.

int zend_parse_parameters_ex(int flags, int num_args TSRMLS_DC, char *type_spec, ...);

The only flag you can pass currently is ZEND_PARSE_PARAMS_QUIET, which instructs the function to not output any error messages during its operation. This is useful for functions that expect several sets of completely different arguments, but you will have to output your own error messages.

For example, here is how you would get either a set of three longs or a string:

long l1, l2, l3; char *s; if (zend_parse_parameters_ex(ZEND_PARSE_PARAMS_QUIET, ZEND_NUM_ARGS() TSRMLS_CC, "lll", &l1, &l2, &l3) == SUCCESS) { /* manipulate longs */ } else if (zend_parse_parameters_ex(ZEND_PARSE_PARAMS_QUIET, ZEND_NUM_ARGS(), "s", &s, &s_len) == SUCCESS) { /* manipulate string */ } else { php_error(E_WARNING, "%s() takes either three long values or a string as argument", get_active_function_name(TSRMLS_C)); return; }

With all the abovementioned ways of receiving function parameters you should have a good handle on this process. For even more example, look through the source code for extensions that are shipped with PHP - they illustrate every conceivable situation.