FreeRTOS-FAT: Passing around file handle pointers

Libraries
1

I need to know if I am overlooking something, or just doing something wrong. I have a function to do a thing, in that function I declare FF_FILE *fileIn and then call another function to open that file and read some header info. fileIn is passed as a function parameter FF_FILE *fileHandle. The debugs in my opening function show the file is being opened and read, and my data is coming in correct, but when it returns and I check the file handle it always fails (!fileIn) and I abort. If I open the file before calling that function (and comment out the ff_fopen in that function) everything works. So why isn’t the handle coming back to me in the original code?

FF_FILE *fileIn;
open_dat_file(&hdrStruct, fileIn);
if (!fileIn)
{
    printf("FILE NOT OPENED\n);
    return 1;
}
....do stuff .....
.
.
.
void open_dat_file(DAT_HDR_T *header, FF_FILE *fileHandle)
{
    ff_fopen(..bla bla bla)
    if (!fileHandle)
    {
        return;
    }
.
.
.
.

I have already made the modifications to get around it, but I just want to make sure I don’t end up with similar issues in the future.

Michael

2

It looks like you are ignoring the pointer to the file returned by ff_fopen.

3

Sorry, that was an error typing up the post. It is actually fileHandle = ff_fopen(bla bla bla).

Michael

4

you pass a pointer into a function, it will not change until you manully return as value.
for example:

int a;
void function( int *p)
{
p=&a;
}
///////////////////////////////

int *value=NULL;
int main(void)
{
fuction(value);
//value is NULL here
}

5

@Yangnaan has correctly identified the issue with your code. You need to return the file handle from the function:

FF_FILE *fileIn = open_dat_file(&hdrStruct);
if (!fileIn)
{
    printf("FILE NOT OPENED\n");
    return 1;
}
....do stuff .....
.
.
.
FF_FILE* open_dat_file(DAT_HDR_T *header)
{
    FF_FILE * handle = ff_fopen(..bla bla bla)
    if (!fileHandle)
    {
        return NULL;
    }
    return handle;
}

If you do not want to use the return value and instead use the parameter, you need to use double pointer.

6

Ugh, yeah stupid mistake, thanks guys. That was at the end of a long day and my thinking wasn’t there.

Michael