use variables from a C generated file

Question

I have generated a C file which contains some arrays with their size as here:

nor.c (generated file)

const float nor[] = {
-0.0972819, 0.906339, -0.4112, -0.056471, 0.340899, -0.938402, -0.284611, 0.269598, -0.919953, 0.04142, -0.149024, -0.987966, 0.12454, -0.702485, -0.700717, 0.0027959, -0.188166, -0.982133 };

const unsigned int nor_size= 18;

when I called this array from my main file as shown here:

extern float nor[nor_size];

I got some error: cannot use nor_size as a const

how to solve this?

thanks

Why don't you generate `const float nor[size]` in the first place? — Devolus, Apr 15 '21 at 11:12
don't use `extern` in your main file, it belongs to header files — gkhaos, Apr 15 '21 at 11:14
Gigo "cannot use nor_size as a const" --> was this the exact error? — chux - Reinstate Monica, Apr 15 '21 at 11:16
Can you create a header file that contains a macro for the size? — Gerhardh, Apr 15 '21 at 11:17
Minor: `-0.0972819` and friends [deserve](https://stackoverflow.com/q/66631288/2410359) an `f` suffix. — chux - Reinstate Monica, Apr 15 '21 at 11:18
In C you should use a `#define` for the size. The use of `const int ...` as numeric constants is a C++ thing that C doesn't support. — Support Ukraine, Apr 15 '21 at 11:20
"when I called this array" make no sense. You don't "call" arrays. And if that file is generated, you should be standing up *two* `extern` (one for the array, and one for the size). e.g `extern const float nor[]; extern const unsigned int nor_size;` — WhozCraig, Apr 15 '21 at 11:21
Do you need the size at all? For an `extern` declaration it is not really required and if you want to calculate the size, you can calculate based on `nor_size` instead of `sizeof`. — Gerhardh, Apr 15 '21 at 11:21
so the linker complains about that: unresolved external symbol — , Apr 15 '21 at 11:44
Take some time and create a [mre] and post exact error messages in the question — klutt, Apr 15 '21 at 11:46
Remember that **StackOverflow is *not* a do-my-homework website** — Basile Starynkevitch, Apr 15 '21 at 12:23
Are you allowed to improve the software generating that C code? — Basile Starynkevitch, Apr 15 '21 at 12:30
Did you add both C files to your project? If you are allowed to improve that software, what about making it create that h file we are talking about as a first step? ;) — Gerhardh, Apr 15 '21 at 13:08
@Gerhardh I have to write some code to add it to .vcxproj.filter — , Apr 15 '21 at 13:10
@BasileStarynkevitch it uses xml format and I've never seen a c++ code that deals with xml format. did you? — , Apr 15 '21 at 13:14
Yes, you can find C++ libraries dealing with XML. See [this](https://stackoverflow.com/q/1542084/841108) question. And you can use other tools for that. — Basile Starynkevitch, Apr 15 '21 at 13:16
can you guide me a little bit? which libraries and which tools? — , Apr 15 '21 at 13:17
No, I have no time for that. You need to take hours in reading documentation. Your teacher is expecting you to read documentation, which you should cite in your homework. If you mention [RefPerSys](http://refpersys.org/) to your teacher, I could help you later. BTW C and C++ are different languages — Basile Starynkevitch, Apr 15 '21 at 13:17
@BasileStarynkevitch it's not a homework, it's a project that I'm working on it alone — , Apr 15 '21 at 13:20
Are you allowed to install a Linux distribution ([Ubuntu](http://ubuntu.com/), [Debian](http://debian.org/), etc...) on your laptop? If yes, backup your important data before, then see [linuxfromscratch](http://linuxfromscratch.org/) — Basile Starynkevitch, Apr 15 '21 at 13:22
Then I cannot help you at all. Good luck. I am coding since 1974 but I never used Windows. I do recommend to meet another programmer in person and discuss with him with your laptop. — Basile Starynkevitch, Apr 15 '21 at 13:25
`const unsigned int nor_size= 18;` should be `const size_t nor_size = sizeof nor / sizeof *nor;` — Lundin, Apr 15 '21 at 13:34
@BasileStarynkevitch " coding since 1974 but I never used Windows" --> Well free bird, I feel a [song](https://www.youtube.com/watch?v=D0W1v0kOELA) coming on. — chux - Reinstate Monica, Apr 15 '21 at 15:42

chux - Reinstate Monica · Answer 1 · 2021-04-15T11:49:57.313

1

how to solve this?

The best would be for the generator of the nor.c file to also generate a corresponding nor.h file

#ifndef NOR_INCLUDE_GUARD
#define NOR_INCLUDE_GUARD

extern const float nor[18];
extern const unsigned int nor_size;

#endif

main.c uses that .h file

// Rather than
// extern float nor[nor_size];

// Include
#include "nor.h"

Also recommend the generator of the nor.c fil to append an f suffix to each constant.

edited Apr 15 '21 at 11:49

answered Apr 15 '21 at 11:37

chux - Reinstate Monica

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I don't have to use h file – Apr 15 '21 at 11:42
@Gigo "I don't have to use h file " --> OK, so you do not have to use a .h file, but it is still the best approach to use one. – chux - Reinstate Monica Apr 15 '21 at 11:45
I think that the c file in not in the path that's why I have an error when calling extern – Apr 15 '21 at 11:48
@Gigo Does "don't have to use h file" mean that you "do not have a h file that you could use" or that you "are not specifically required to use h file"? – Gerhardh Apr 15 '21 at 13:06
I'm not required to use . file – Apr 15 '21 at 13:07
1

@Gigo Then after it was mentioned a few times, you are also not prevented from using a h file. Then, what stops you from doing it? – Gerhardh Apr 15 '21 at 13:09

Basile Starynkevitch · Answer 2 · 2021-04-15T12:36:54.090

0

In your main.c remove ~~extern float nor[nor_size];~~ then add

extern const float nor[];
extern const unsigned int nor_size;

and use them as appropriate. Indeed, nor_size might then be loaded (in processor registers at the machine code level) several times.

For more, read this C reference, and later some C standard like n1570 or better.

If you are allowed to compile all your C (both handwritten and generated) code with some recent GCC compiler (or cross-compiler), invoke it at least with -Wall -Wextra -g options.

don't forget to read the documentation of your C compiler!

You also need to understand what is your linker, and read its documentation. Maybe it could be GNU binutils.

You could use some static source code analyzer, like Clang static analyzer, or Frama-C, or Bismon. FYI, Bismon has 24604 lines of generated C code, and the Bigloo compiler has a lot of them too.

^{for Frama-C or Bismon, contact me by email to basile.starynkevitch@cea.fr and mention the URL of your question}

Read also a good C programming book, like Modern C

In 2021, you could be interested by the DECODER project. It is strongly related to your question.

An interesting book describing a software which generates all the half-million lines of code of its C source (available here) is Pitrat's Artificial Beings: the Conscience of a Conscious Machine (ISBN 978-1848211018). You could enjoy reading that book.

See also this answer about generating C code.

You could also be interested by GNU bison. It is a free software parser generator, mostly written in C, and generates C code. My recommendation is to download its source code and take inspiration from it.

By experience, when you are generating C code, it is easier to improve the generator (so that the generated C code compiles cleanly without warnings) that to change the generated C code. But do document well your C code generator. Read about partial evaluation techniques.

edited Apr 15 '21 at 12:36

answered Apr 15 '21 at 11:43

Basile Starynkevitch

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it doesn't work, I think that the compiler doesn't see my generated c file – Apr 15 '21 at 11:45
This means you are using your compiler wrongly. Did you read the documentation of your compiler?. – Basile Starynkevitch Apr 15 '21 at 11:46
I use the visual studio compiler (VS2019) – Apr 15 '21 at 11:49
why I have to read its doc, I write the code and then the compiler will do the job – Apr 15 '21 at 11:53
Your question is showing that the compiler is not doing the job you expect. – Basile Starynkevitch Apr 15 '21 at 11:54
I have to link the generated c file with my path i think – Apr 15 '21 at 11:57
yes but what do you think about what I said? – Apr 15 '21 at 12:01
I was not able to understand what you have said, and from my perspective, you said nothing and did not write enough. – Basile Starynkevitch Apr 15 '21 at 12:04
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There is no need to include a huge appendix with barely on-topic tool recommendations to every post. Newbies will _not_ benefit from static analysers and other more advanced tools, quite the opposite. – Lundin Apr 15 '21 at 13:32
I disagree. Static analyzer tools are useful to newbies. Exactly like is useful the `-Wall -Wextra` options to `gcc`; and when coding a C code generator, trying to *avoid* warnings from GCC (or from some static analyzer tool) is a good habit to have. Look BTW into the coding rules related to bootstrapping GCC when contributing to it. – Basile Starynkevitch Apr 15 '21 at 19:20

use variables from a C generated file

2 Answers2

don't forget to read the documentation of your C compiler!

Read also a good C programming book, like Modern C

See also this answer about generating C code.