Dynamic function calls at runtime (va_list) - c++

Question

There is a way in C to obtain a dynamic length argument list with va_list, as described here:
http://www.cprogramming.com/tutorial/c/lesson17.html
That quite simple, but most times in C++ not needed. I am currently building a top level wrapper class for encapsulating some Zend functionality.
Anyway, I do need to make a call to such a dynamic function like printf from a normal function dynamically.
I mean the reverse way of the example described above, here is waht I got so war, maybe this explains my idea a little better:
void ZendParams::setRequired( int &Var )
{
// save every var pointer to a stack
// and save the type with it. (if needed, does not seems to be)
// after call to ZendParams::fetch()
// the values are stored in the passed variables
this->_params.push_back( (void*) &Var );
this->_paramStr.append( 'i' );
}
size_t ZendParams::fetch()
{
if ( zend_parse_parameters(
ZEND_NUM_ARGS() TSRMLS_CC, ,
this->_paramStr.c_str(),
...
) !== FAILURE)
{
}
return 0;
}
So I want to make the call to zend_parse_parameters dynamically.
The base idea is to add pointer to vars in a list and pass them to the zend function (as reference) dynamically.
I thought there must be a way to do this with va_list , too.
But how?
To get it more simple, I am using this example:
list<int> myList;
myList.push_back(1);
myList.push_back(5);
myList.push_back(10);
myList.push_back(37);
myList.push_back(42);
double function avg( int num, ... )
va_list arguments;
int sum = 0;
va_start ( arguments, num );
for ( int x = 0; x < num; x++ )
{
sum += va_arg ( arguments, int );
}
va_end ( arguments );
return sum / num;
}
I want to call avg with all numbers I got in the list. I took the example function from the tutorial mentioned above, but it should show up what I mean in a very simple way.
However, I can not change the function called, as it is part of the zend framework.
Is there any way in C or C++ to do this?
My 2nd approach:
template <typename... Arguments>
size_t Zend::getMethodParams( string paramStr, Arguments... Args )
{
if ( zend_parse_parameters(
ZEND_NUM_ARGS() TSRMLS_CC, ,
paramStr.c_str(),
Args...
) == FAILURE)
{
return 0;
}
}
To be called like this (to get the defined 3 Parameters):
string My1stParam;
int My2ndParam;
int My3rdParam;
Zend::getMethodParams<string, int, int>( "sii", &My1stParam, &My2ndParam, &My3rdParam );
I think that should work, but there is one hard issue with that:
The zend_parse_parameters function returns 2 values for a string (c-style string!):
- a char pointer and
- the string length.
So I would either have to call it that way:
char* My1stParam_str;
int My1stParam_length
int My2ndParam;
int My3rdParam;
Zend::getMethodParams<string, int, int>( "sii", &My1stParam_str, &My1stParam_length, &My2ndParam, &My3rdParam );
string My1stParam;
My1stParam.assign(My1stParam_str, My1stParam_length);
Anyway, that was what I wanted to prevent.
Or I would have to modify the list of arguments passed to the zend_parse_parameters function to do these additional steps internally.
I am hoping to be able to call it at least in that way:
string My1stParam;
int My2ndParam;
int My3rdParam;
Zend::getMethodParams<string, int, int>( "sii", &My1stParam, &My2ndParam, &My3rdParam );
So say this clearly: The parameters are known at compile time, but the function call will be very different within all occurrences in the later sourcecode.

Answer 1

I found a way around this within the zend framework. I did indeed search for such a solution before, but it seems to be not very good documented ( n.m. already mentoined, that there is no zend internal way like a va_list taking function ).
But there is indeed one!
For everyone else stucking with this problem:
long arg;
zval ***args;
int i, argc = ZEND_NUM_ARGS( );
if (zend_parse_parameters(1 TSRMLS_CC, "l", &arg) == FAILURE) return;
array_init(return_value);
add_index_long(return_value, 0, arg);
if(argc>1) {
args = (zval ***)emalloc(argc * sizeof(zval **));
if(zend_get_parameters_array_ex(argc, args) == FAILURE) {
efree(args);
return;
}
for(i = 1; i < argc; i++) {
zval_add_ref(args[i]);
add_index_zval(return_value,i, *args[i]);
}
efree(args);
}
That is the solution ;)
This snippet, found on http://docstore.mik.ua/orelly/webprog/php/ch14_07.htm parses all parameters dynamically into the c representation of an PHP array.