C-Structure | Course labs for Introduction to structured programming | Learning library

I'm currently exploring modding using Fabric. About a month ago, I made a mod that worked just fine, both when run from the debugger in VSCode and when compiled and run on a real Minecraft installation. I have added a few things since I compiled it, but now the newly compiled version crashes the game upon loading. However, strangely, there is no crash when run from the debugger in VSCode.

Here is ExampleMod.Java:

I have a c-structure that I want to return from a c-function to c# and that structure contains an array of int and a length. So basically

The C99 standard tells us:

There may be unnamed padding within a structure object, but not at its beginning.

and

There may be unnamed padding at the end of a structure or union.

I am assuming this applies to any of the C++ standards too, but I have not checked them.

Let's assume a C/C++ application (i.e. both languages are used in the application) running on an ARM Cortex-M would store some persistent data on a local medium (a serial NOR-flash chip for instance), and read it back after power cycling, possibly after an upgrade of the application itself in the future. The upgraded application may have been compiled with an upgraded compiler (we assume gcc).

Let's further assume that the developer is lazy (that's not me, of course), and directly streams some plain C or C++ structs to flash, instead of first serializing them as any paranoid experienced developer would do.

In fact, the developer in question is lazy, but not totally ignorant, since he has read the AAPCS (Procedure Call Standard for the Arm Architecture).

His rationale, besides laziness, is the following:

• He does not want to pack the structs to avoid misalignment problems in the rest of the application.
• The AAPCS specifies a fixed alignment for every single fundamental data type.
• The only rational motivation for padding is to achieve proper alignment.
• Therefore, he thinks, padding (and therefore member offsetof and total sizeof) is fully determined for any C or C++ struct by the AAPCS.
• Therefore, he further reasons, there is no way my application would not be able to interpret some read back data that an earlier version of the same application would have written (assuming, of course, that the offset of the data in flash memory has not changed between writing and reading).

However, the developer has a conscience and he is a little worried:

• The C standard does not mention any reason for padding. Achieving proper alignment may be the only rational reason for padding, but compilers are free to pad as much as they want, according to the standard.
• How can he be sure that his compiler really follows the AAPCS?
• Could his assumptions suddenly be broken by some apparently unrelated compiler flag that he would start using, or by a compiler upgrade?

My question is: how dangerously does that lazy developer live? In other words, how stable is padding in C/C++ structs under the assumptions above?

Two weeks after this question was asked, the only answer that has been received does not really answer the asked question. I have also asked the exact same question on an ARM community forum, but got no answer at all.

I however choose to accept 3246135 as the answer because:

1. I take the absence of proper answer as very relevant information for this case. The correctness of solutions to software problems should be obvious. The assumptions made in my question may be true, but I cannot easily prove it. Additionally, if the assumptions are incorrect, the consequences, in the general case, could be catastrophic.

2. Compared to the risk, the burden on the developer when using the strategy exposed in the answer seems very reasonable. Assuming a constant endianness (which is quite easy to enforce), it is a hundred percent-safe (any deviation will generate an error at compile-time) and it is much lighter than a full-blown serialization. Basically, the strategy exposed in the answer is a mandatory minimum price to pay in order to make one's C/C++ structs persistent independently of any ABI.

If you are a developer asking yourself the question above, please do not be lazy, and use instead the strategy exposed in the accepted answer, or an alternative strategy that guarantees a constant padding across software releases.

I am getting a C-structure from C-client to python server over UDP socket. I am trying to read the message from it. I am having hard time figuring out the format for unpacking and also, printing the message. Can someone please help.

This is python server which receives the message form C client.

I'd like to edit public function generate_product_data from woocommerce/includes/class-wc-structured-data.php

Inside this function:

I'm trying to create a self-expanding array of a structure. I saw the questions here, here and here but the answers didn't seem to apply to my situation.

I have had pretty good luck using this technique using an array of strings, but using a structure doesn't work. Below is the code:

My c++ code has to work with an underlying c-library. I have a c++ object that looks somewhat like this:

I'm trying to interact with an old C terminal app/library from Swift. I've successfully integrated the source code and bridged the headers from C to Swift. The code compiles and runs, I can access all functions from C - library into swift.

There is a structure in C - library which I need to initialize[Function already exists which takes pointer] and assign values to structure variables[Manually].

C-structure:

I ran the sample code on TutorialsPoint under the title of "C-Structure" and did some experiment. I tried to print the address of the pointer to a struct and addresses of some components in the struct, here is the struct: