Creating freestanding applications

Freestanding applications are C modules that run either:

• Without z/OS® Language Environment® and the z/OS XL C library (using EDCXSTRT)
• Without z/OS Language Environment but with the z/OS XL C library functions (using EDCXSTRL)

Three initialization routines are provided by SPC for building freestanding applications:

EDCXSTRT

For building completely freestanding applications. The applications can use no z/OS XL C runtime library functions and can have no z/OS Language Environment attachment.

EDCXSTRL

For building applications that use z/OS XL C runtime library functions but have no z/OS Language Environment attachment.

EDCXSTRX

This routine accepts a parameter to choose whether your application should behave as if it was initialized with either EDCXSTRT or EDCXSTRL. This parameter is described further in Setting up a C environment with preallocated stack and heap.

Certain restrictions apply to freestanding applications initialized by the routines EDCXSTRT, EDCXSTRL, and EDCXSTRX. These restrictions are as follows:

• They cannot perform interlanguage calls, except with assembler language routines that preserve register 12 and use the IBM®-supplied macros for entry and exit.
• The parameters received by the main() function (normally argc and argv) are undefined. __xregs() (described in __xregs() — Get Registers on Entry) can be used to examine the parameters passed by the calling environment.
• They cannot do arithmetic using long double variables on pre-XA machines (that is, on machines that do not support the DXR instruction).