arrays, structs, dlls, functions...

This is a discussion on arrays, structs, dlls, functions... within the C Programming forums, part of the General Programming Boards category; Hi, I am very much stuck in the following issue. Any help is very much appreciated! Basically I have a ...

  1. #1
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    Mar 2011
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    2

    arrays, structs, dlls, functions...

    Hi, I am very much stuck in the following issue. Any help is very much appreciated!

    Basically I have a program wich contains an array of structs and I am getting a segmentation error when I call an external function. The error only happens when I have more than 170 items on the array being passed.

    Nothing on the function is processed. The program stops exactly when accessing the function.

    Is there a limit for the size of the parameters that are passed to external functions?

    Main.c
    Code:
    struct ratingObj {
    	int uid;
    	int mid;
    	double rating;
    };
    
    void  *FunctionLib;		/*  Handle to shared lib file	*/
    void (*Function)();		/*  Pointer to loaded routine	*/
    const char *dlError;		/*  Pointer to error string	*/
    
    int main( int argc, char * argv[]){
    // ... some code ...
    	struct ratingObj movies[listSize];
    // ... more code ...
    	FunctionLib = dlopen("dll.so", RTLD_LAZY);
    	dlError = dlerror();
    	if( dlError ) exit(1);
    	Function = dlsym( FunctionLib, "getResults");
    	dlError = dlerror();
    	(*Function)( moviesToRate, listSize );
    // .. more code
    }
    library.c
    Code:
    struct ratingObj {
    	int uid;
    	int mid;
    	double rating;
    };
    
    typedef struct ratingObj ratingObj;
    
    void getResults(struct ratingObj *moviesToRate, int listSize);
    
    void getResults(struct ratingObj *moviesToRate, int listSize){
    // ... more code
    }

  2. #2
    cas
    cas is offline
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    Sep 2007
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    It's hard to say for sure without seeing the code. At the very least, you should declare the parameter types in your function pointer:
    Code:
    void (*Function)(struct ratingObj *, int);
    The more type safety, the better.
    Is there a limit for the size of the parameters that are passed to external functions?
    There's no special limit beyond what limits you'd normally have in calling a function; but you're passing the same size objects no matter how many items there are. Your pointer will always be the same size, as will your int.

    Have you tried running the program under a debugger? That should be your very first move when you have a segfault.

  3. #3
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    Mar 2011
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    Talking

    Thanks cas. Attached the gdb debugger and found several issues. I converted all the main arrays to use malloc and now the code is more reliable.

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