use cmake add_definition value in fortran

Question

I'd like to include a flag such as -DMY_FLAG=ONETWOTHREE in the CMake call, i.e. make .. -DMY_FLAG=ONETWOTHREE, and get the value of MY_FLAG in the fortran code. I'm using add_definitions("-DMY_FLAG=${MY_FLAG}") to pass MY_FLAG to make.

Currently, when I do something like
write(*,*) MY_FLAG

I get this compiler error:
Error: Symbol 'ONETWOTHREE' at (1) has no IMPLICIT type

Can the -D flags be cast to a type in fortran? It looks like MY_FLAG is somehow defined at compile time, but it has no type.

Then this is a problem with the source code, which is what the below answer seems to say also. — Matthew Schuchard, Aug 13 '17 at 20:12

score 3 · Accepted Answer · answered Aug 12 '17 at 13:47

3

When using a preprocessor, the final source file must be valid Fortran. In the present situation,

write(*,*) ONETWOTHREE

is not valid because there is not variable named ONETWOTHREE.

Solutions:

Define the variable earlier:
```
integer ONETWOTHREE
ONETWOTHREE = 5
```
Do not use ONETWOTHREE but an actual value. Example for an integer:
```
-DMY_FLAG=123
```
so that the corresponding line will be
```
write(*,*) 123
```

Of course, it would be useful if you could provide us with the intention behind the usage of the preprocessor here.

answered Aug 12 '17 at 13:47

Pierre de Buyl

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apparently cmake wants a specific syntax when using `add_definitions`. does NOT work: `add_definitions("-DMY_FLAG=${MY_FLAG}")`. does work: `add_definitions(-DMY_FLAG="${MY_FLAG}")`. This is for a string value for `MY_FLAG`. For a numeric value, no quotes are necessary. – raf Aug 15 '17 at 13:47
This is in line with the [documentation](https://cmake.org/cmake/help/latest/command/add_definitions.html): overall quoting inside `add_definitions` is not to be used. The quotes are for the replacement in the source code as strings are quoted in Fortran. – Pierre de Buyl Aug 16 '17 at 07:30

use cmake add_definition value in fortran

1 Answers1