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MSP430FR2355: Is the following use of extern with respect to k legal in the following example?

Steve Wenner
Genius 3190 points
Part Number: MSP430FR2355

Assuming I link the library correctly to the executable project can I define k in the library then use in the executable as seen below?  Is this legal?

Project A (library): libtest.libc

libA.c

#include "lib.h"

int k = 0;

libB.c

#include "lib.h"

m = k+1;

lib.h

extern int k;

Project B (executable): main.c

#include "lib.h"


r = k*2

Thanks

  • 0
    Guru 35680 points

    Yep, that is the way to do it.

  • 0
    Genius 3190 points

    Part Number: MSP430FR2355

    A trickier question and the use of static....this is hypothetical and I'm trying to understand. If I have a lib.libc project with multiple c source files and I place 

    static int k = 0;

    at the global scope level of one of the c source files because I want the value k to be retained not only across functions within the source file but across source files within the project.  How will the second source file in the library see this?  Do I use static and extern together somehow or should I be placing the definition in an header file for the project?

  • 0 in reply to Steve Wenner
    Guru 35680 points

    Unfortunately, the meaning of static depends on the context.

    It is rarely needed in global definitions out of a function scope.

    It really just matters in a function definition to state that its value should be retained between calls. This is what automatically happens for global variables.

  • 0 in reply to Keith Barkley
    Genius 3190 points

    If however you have multiple functions within a file and use static outside these then they all have access to it AND no one outside the file can see it, correct?

    If so my question I guess becomes if you have multiple c source files and a header within a library project, what is the best mechanism for creating 'private' variables SUCH that all the library source files can see them and use them BUT the application code project will not see these variables (or not have access to them) once you include the library header file into that executable project?

  • 0 in reply to Steve Wenner
    TI__Guru 60361 points

    Hi Steve,

    I'm reading along here and wanted to know if you got your question answered?

  • 0 in reply to Dennis Lehman
    Genius 3190 points

    Hi Dennis....

    Yes I believe all is good here....

    Thanks

    Steve

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