Why Does 'long double' Occupy 12 Bytes on My 32-bit Windows XP System?

Clarifying the Discrepancy between 'long double' and 'double' Data Types

Despite the common understanding that 'long double' typically occupies 8 bytes, the poster encounters a peculiar scenario where 'long double' claims 12 bytes on their 32-bit Windows XP system. To unravel this enigma, let's delve into the underlying reasons.

According to Wikipedia, on the x86 architecture (which includes Windows XP), most compilers opt to implement 'long double' as an 80-bit extended precision type. However, to maintain efficient data structure alignment, this type may be stored as 12 bytes (or even 16 bytes) in some cases.

Additionally, certain compilers go beyond the 80-bit type and implement 'long double' as a 128-bit quadruple precision format. This advanced format is not widely adopted and is typically implemented in software, rather than being natively supported by hardware.

Therefore, the answer lies in the compiler's discretion. While 'long double' generally aligns with the 80-bit extended precision type, compilers are free to extend its storage capacity to 12 or even 16 bytes for alignment purposes. As a result, the extended storage capacity potentially allows for a wider range of values to be stored in 'long double' compared to 'double'.

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