-qldbl128, -qlongdouble

Description

Increases the size of long double type from 64 bits to 128 bits.

Syntax

Read syntax diagramSkip visual syntax diagram        .-noldbl128----.
>>- -q--+-ldbl128------+---------------------------------------><
        +-nolongdouble-+
        '-longdouble---'

See also #pragma options.

Notes

The -qlongdouble option is the same as the -qldbl128 option.

Separate libraries are provided that support 128-bit long double types. These libraries will be automatically linked if you use any of the invocation commands with the 128 suffix (xlC128, xlc128, cc128, xlC128_r, xlc128_r, or cc128_r). You can also manually link to the 128-bit versions of the libraries using the -lkey option, as shown in the following table:

Default (64-bit) long double 128-bit long double
Library Form of the -lkey option Library Form of the -lkey option
libC.a -lC libC128.a -lC128
libC_r.a -lC_r libC128_r.a -lC128_r

Linking without the 128-bit versions of the libraries when your program uses 128-bit long doubles (for example, if you specify -qldbl128 alone) may produce unpredictable results.

The -qldbl128 option defines __LONGDOUBLE128.

The #pragma options directive must appear before the first C or C++ statement in the source file, and the option applies to the entire file.

Example

To compile myprogram.c so that long double types are 128 bits, enter:

xlc++ myprogram.c -qldbl128 -lC128

or:

xlc++128 myprogram.c

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