How to avoid structure padding?

Question

I'm curious to know about how #pragma will help to avoid stucture padding (please give me one programme to understand it).

By default compilers will allocate memory in an aligned manner. So by avoiding structure padding what will be the benifit programmer will get? When is it neccessary to avoid structure padding?

It's not part of the C standard, but compilers have ways to handle it as extensions. However, different compilers do it differently, and if you want help you have to tell us what compiler you are using. You might also want to tell us *why* you want it. — Some programmer dude, Feb 05 '15 at 09:54
Advice: you don't want it, you don't need it. Avoid it, unless it is absolutely necessary. — joop, Feb 05 '15 at 09:54
see this http://stackoverflow.com/questions/5397447/struct-padding-in-c — VolAnd, Feb 05 '15 at 09:54
`#pragma pack (1)` to disable byte padding and `#pragma pack ()` to reenable it. — mch, Feb 05 '15 at 09:58

score 2 · Accepted Answer · answered Feb 05 '15 at 10:02

The techniques depend on compiler.

The benefits are usually not much, other than potentially reducing the amount of memory consumed by your program. That benefit is only worth while on machines with few resources (e.g. memory) which means it is rarely needed with modern hardware.

In practice, the cost is reduced performance or hardware exceptions. The common purposes of padding are performance and avoiding hardware exceptions, by aligning struct members in a way that suits the host system. Disallowing padding basically turns off all the benefits of padding.

Saving a few bytes, or even a few kilobytes, is rarely worth the impact in terms of performance or more error conditions. If you are doing certain types of development (e.g. on embedded system with limited resources) it might be worthwhile, but even then not always.

In embedded system there are more benefits of structure packing than just saving space. For example you may have received a packed byte array through communication and want to interpret it. Instead of copying and converting byte-by-byte you can just cast it to a struct and use the fields. Of course you have to make sure Endianness and MSB are identical with message and processor allow unaligned access. — ifyalciner, Jun 07 '17 at 15:28

score 1 · Answer 2 · answered Feb 05 '15 at 09:57

1.Structure Padding is avoided mostly in case of resource critical embedded systems.In this case RAM is saved by packing the structure members on the expense of code memory(More Instructions are needed to access the packed structure member).

In some cases an array of bytes is mapped to structure members for ease of accessing.

score 1 · Answer 3 · answered Dec 20 '17 at 11:03

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structure paddding can be avoided by using a preprocessor directive #pragma 1 the compiler will alocate memory in multiples of one

answered Dec 20 '17 at 11:03

anil

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How to avoid structure padding?

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