HP UX Fortran Software manual Creating demand-loadable executables, Creating shared executables

The value of x in double_it: 3.0 x = 6.0

The next command line does not use the-Doption, so that DEBUGis undefined, causing cpp to remove the PRINTstatements from the source text that is passed to the compiler:

$ f90 +cpp=yes cpp_direct.f90

Here is the output from the nondebugging version of the program:

$ a.out

Enter a real number: 3.3 x = 6.6

Saving the cpp output file

By default, the f90command discards the source text as processed by cpp after compilation. However, you can preserve this text by compiling with the +cpp_keepoption. If the source file has the .For .fextension, the output from cppis written to a file with the same name but with the

.iextension. If the source file extension is .f90, the output file has the .i90extension.

Here is the previous command line to preprocess and compile cpp_direct.f90, with the addition of the +cpp_keep option:

$ f90 +cpp_keep +cpp=yes cpp_direct.f90

After the PRINTstatements have been removed, the resulting output file looks like this:

$ cat cpp_direct.i90

#1 "cpp_direct.f90" PROGRAM main

REAL :: x

WRITE (6, FMT='(A)', ADVANCE='NO') 'Enter a real number:' READ *, x

PRINT *, 'x =', double_it(x) END PROGRAM main

REAL FUNCTION double_it(arg) REAL :: arg

double_it = 2.0 * arg END FUNCTION double_it Compiling

Creating demand-loadable executables

By default, the loader loads the entire code for an executable program into virtual memory. For very large programs, this can increase startup time. You can override this default by causing the linker to mark your program demand load. A demand-loadable program is loaded into memory a page at a time, as it is accessed.

Use the +demand_loadoption to make your program demand loadable, as follows:

$ f90 +demand_load prog.f90

The f90 command passes this option to the linker, which marks the executable program demand load.

Demand loading allows a program to start up faster because page loading can be spread across the execution of the program. The disadvantage of demand loading is that it can degrade performance throughout execution.

Creating shared executables

By default, the linker marks an executable program as shared. A shared executable is shareable by all processes that use the program. The first process to run the program loads its code into virtual memory. If the program is already loaded by another process, then a process shares the code with the other process.

62 Compiling and linking