typedef function pointer -> initialization from incompatible pointer type

Question

I'm having trouble understanding the cause of this warning:

menu-file-select.c:41:29: warning: initialization from incompatible pointer type

The offending code is:

typedef int (*FileSelectFilter)(const char*, struct dirent*);

typedef struct {
    const char *dir; //the directory path to read
    const char *out; //where to copy the selected path
    int outLen; //length of out buffer
    FileSelectFilter *filter; //optional filter function
} FileSelectParams;

void showFileSelectMenu(FileSelectParams *params) {
    /* ... */
    FileSelectFilter filter = params->filter; // <-- warning generated here.
    if(filter && !filter(path, ent)) continue;
    /* ... */
}

int main(int argc, char **argv) {
    /* ... */
    FileSelectParams fsel = {
        .dir    = setting.lastpath,
        .out    = RomPath,
        .outLen = sizeof(RomPath) - 1,
        .filter = FileSelectFilter_Roms,
    };
    showFileSelectMenu(&fsel);
    /* ... */
}

int FileSelectFilter_Roms(const char *path, struct dirent *file) {
    /* ... */
}

As far as I can tell, FileSelectFilter_Roms matches the FileSelectFilter typedef, so I don't understand why I'm being told the type is incompatible. The program seems to work anyway, but having this warning here bothers me.

FileSelectFilter is already a pointer to a function (as per typedef). So in FileSelectParams, filter is defined as a pointer to a pointer to a function - drop the * ! — isedev
– isedev, Commented Sep 30, 2014 at 12:29
As an alternative (if you don't like typedefed pointers), you can typedef the function rather than a pointer to it: typedef int FileSelectFilter(const char *, struct dirent *); — mafso
– mafso, Commented Sep 30, 2014 at 12:43

isedev · Accepted Answer · 2014-09-30 12:35:58Z

4

You have defined FileSelectFilter as a pointer to a function in the typedef:

typedef int (*FileSelectFilter)(const char*, struct dirent*);

In FileSelectPararms, you define filter member as:

FileSelectFilter *filter;

This means that filter is actually a pointer to a pointer to a function. This is the reason why you are getting the error in the assignment FileSelectFilter filter = params->filter;.

The filter member should simply be defined as:

FileSelectFilter filter;

answered Sep 30, 2014 at 12:35

isedev

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