Why padding in structure

So, 32 bit processor always reads 4 bytes at a time and 64 bit processor always reads 8 bytes at a time. This concept is very useful to increase the processor speed. To make use of this advantage, memory is arranged as a group of 4 bytes in 32 bit processor and 8 bytes in 64 bit processor. Below C program is compiled and executed in 32 bit compiler.

Please check memory allocated for structure1 and structure2 in below program. In above program, memory for structure1 is allocated sequentially for first 4 members. Range of this 4 byte package is from to Addresses and only is available in this package. Due to the change in the order, the output would be different in both the cases.

In the previous case, the output was 8 bytes, but in this case, the output is 12 bytes, as we can observe in the below screenshot. The structural padding is an in-built process that is automatically done by the compiler. Sometimes it required to avoid the structure padding in C as it makes the size of the structure greater than the size of the structure members.

In the above code, we have used the pragma pack 1 directive to avoid the structure padding. If we do not use this directive, then the output of the above program would be 16 bytes.

But the actual size of the structure members is 13 bytes, so 3 bytes are wasted. To avoid the wastage of memory, we use the pragma pack 1 directive to provide the 1-byte packaging. JavaTpoint offers too many high quality services.

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