What are the most common naming conventions in C?

Question

The most important thing here is consistency. That said, I follow the GTK+ coding convention, which can be summarized as follows:

1. All macros and constants in caps: MAX_BUFFER_SIZE, TRACKING_ID_PREFIX.
2. Struct names and typedef's in camelcase: GtkWidget, TrackingOrder.
3. Functions that operate on structs: classic C style: gtk_widget_show(), tracking_order_process().
4. Pointers: nothing fancy here: GtkWidget *foo, TrackingOrder *bar.
5. Global variables: just don't use global variables. They are evil.
6. Functions that are there, but shouldn't be called directly, or have obscure uses, or whatever: one or more underscores at the beginning: _refrobnicate_data_tables(), _destroy_cache().

"Struct pointers" aren't entities that need a naming convention clause to cover them. They're just struct WhatEver *. DON'T hide the fact that there is a pointer involved with a clever and "obvious" typedef. It serves no purpose, is longer to type, and destroys the balance between declaration and access.

You know, I like to keep it simple, but clear... So here's what I use, in C:

• Trivial Variables: i,n,c,etc... (Only one letter. If one letter isn't clear, then make it a Local Variable)
• Local Variables: camelCase
• Global Variables: g_camelCase
• Const Variables: ALL_CAPS
• Pointer Variables: add a p_ to the prefix. For global variables it would be gp_var, for local variables p_var, for const variables p_VAR. If far pointers are used then use an fp_ instead of p_.
• Structs: ModulePascalCase (Module = full module name, or a 2-3 letter abbreviation, but still in PascalCase.)
• Struct Member Variables: camelCase
• Enums: ModulePascalCase
• Enum Values: ALL_CAPS
• Public Functions: ModulePascalCase
• Private Functions: PascalCase
• Macros: PascalCase

I typedef my structs, but use the same name for both the tag and the typedef. The tag is not meant to be commonly used. Instead it's preferrable to use the typedef. I also forward declare the typedef in the public module header for encapsulation and so that I can use the typedef'd name in the definition.

Full struct Example:

typdef struct UtilsExampleStruct UtilsExampleStruct;
struct UtilsExampleStruct{
    int var;
    UtilsExampleStruct *p_link;
};

Well firstly C doesn't have public/private/virtual functions. That's C++ and it has different conventions. In C typically you have:

• Constants in ALL_CAPS
• Underscores to delimit words in structs or function names, hardly ever do you see camel case in C;
• structs, typedefs, unions, members (of unions and structs) and enum values typically are in lower case (in my experience) rather than the C++/Java/C#/etc convention of making the first letter a capital but I guess it's possible in C too.

C++ is more complex. I've seen a real mix here. Camel case for class names or lowercase+underscores (camel case is more common in my experience). Structs are used rarely (and typically because a library requires them, otherwise you'd use classes).