Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>If you can, use struct "interfaces":</p> <pre><code>struct Device { int (*read_temp)(int*, Device*); } *dev; </code></pre> <p>call it:</p> <pre><code>dev-&gt;read_temp(&amp;ret, dev); </code></pre> <p>If you need additional arguments, pack them inside Device</p> <pre><code>struct COMDevice { struct Device d; int port_nr; }; </code></pre> <p>and when you use this, just downcast.</p> <p>Then, you'll create functions for your devices:</p> <pre><code>int foo_read_temp(int* ret, struct Device*) { *ret = 100; return 0; } int com_device_read_temp(int* ret, struct Device* dev) { struct COMDevice* cdev = (struct COMDevice*)dev; /* could be made as a macro */ ... communicate with device on com port cdev-&gt;port_nr ... *ret = ... what you got ... return error; } </code></pre> <p>and create the devices like this:</p> <pre><code>Device* foo_device= { .read_temp = foo_read_temp }; COMDevice* com_device_1= { .d = { .read_temp = com_read_temp }, .port_nr = 0x3e8 }; COMDevice* com_device_1= { .d = { .read_temp = com_read_temp }, .port_nr = 0x3f8 }; </code></pre> <p>You'll pass the Device structure around to function that need to read the temperature.</p> <p>This (or something similar) is used in the Linux kernel, exceptthat they don't put the function pointers inside the structs, but create a special static struct for it and stor pointer to this struct inside the Device struct. This is almost exactly how object oriented lingages like C++ implement polymorphism.</p> <p>If you put the functions in a separate compilation unit, including the Device struct that refer to them, you can still save space and leave them out while linking.</p> <p>If you need different types of arguments, or fewer arguments, just forget it. This means you cannot design a common interface (in any sense) for things you want to change, but without a common interface, no changeable implementation is possible. You can use compile-time polymorphism (eg. typedefs &amp; separate compilation units for different implementations, one of which would be linked in your binary), but it still has to be at least source-compatible, that is, be called in the same way.</p>
    singulars
    1. This table or related slice is empty.
    1. POBest strategy to call an arbitrary function without using JMP or LCALL
      singulars
      1. PTQuestion
    1. PTAnswer
    1. USjpalecek
    1. USjpalecek
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. COSorry. I edited it to make it more C.
      singulars
      1. PO
      1. USjpalecek
    2. COC structs can have members of any type a variable can have, including function pointers. (If you don't believe it, just try it, or look into Linux source code.) What you say about C++ struct/class is almost true, but is totally irrelevant to your question AND my answer - not sure why you mention it.
      singulars
      1. PO
      1. USjpalecek
    3. COSorry, I misread your code, it seamed you had a function, not a function-pointer, in that struct. How is a called function going to know about the additional arguments that you've encapsulated on that second struct? Your point about common interfaces being a requirement for a non-changed implementation is correct. So, what I'm trying here is to find a way to step outside the "normal" C signature for a function (return, number of args and their types) and come up with something more flexible (but probably less obvious)
      singulars
      1. PO
      1. USjpinto3912
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload