Re: How do I create a function in my library for passing user callback function

On Apr 13, 12:39 pm, "Angus" <nos...@xxxxxxxxx> wrote:
Hello

I am writing a library which will write data to a user defined callback
function. The function the user of my library will supply is:

int (*callbackfunction)(const char*);

In my libary do I create a function where user passes this callback
function? How would I define the function?

I tried this

callbackfunction clientfunction;

void SpecifyCallbackfunction(cbFunction cbFn)
{
clientfunction = cbFn;

}

Then called like this:
clientfunction(sz); // sz is a C-string.

But program crashes with access violation when attempt to call
clientfunction

What am I doing wrong?

Based on what you've written here, it sounds like you want to
"register" the callback so it can be called by other functions within
the library: is that correct? If so, here's one approach:

/* Library header file */
#ifndef LIB_H
#define LIB_H
/**
* Create a typedef for the function pointer type
*/
typedef int (*callback)(const char *);

/**
* Register the callback function
*/
void SpecifyCallbackfunction(callback f);

/**
* Other library functions that will use the callback
*/
void L1(const char *foo);
void L2(void);

#endif

/**
* Library implementation file
*/

/**
* File-scope global for callback
*/
static callback g_callback;

void SpecifyCallbackFunction(callback f)
{
g_callback = f;
}

void L1(const char *foo)
{
int bar = g_callback(foo);
...
}

void L2(void)
{
int bar = g_callback("DUMMY");
...
}

/**
* main
*/

#include "library.h"

int blah(const char *bletch)
{
int retVal;
retVal = /* result of doing something with bletch */
return retVal;
}

int main(void)
{
SpecifyCallbackFunction(blah);
L1("blurga");
L2();
...
return 0;
}

HTH.
.

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