编译const GdkPixdata：“错误：初始化元素不是常量”

Question

I'm into a problem that I can't really understand.
I want to "include" directly into my C code a series of icons. Using the tool gdk-pixbuf-csource (with --struct option) I produced a file that initializes a 'const' pixdata structure for each image. And example of an encoded image is this:

const GdkPixdata pixdata_flipH = {
   0x47646b50, /* Pixbuf magic: 'GdkP' */
   24 + 479, /* header length + pixel_data length */
   0x2010002, /* pixdata_type */
   64, /* rowstride */
   16, /* width */
   16, /* height */
   /* pixel_data: */
   "\257\0\0\0\0\1\0\0\0\1\203\0\0\0\0\2\0\0\0\2\40J\207E\202\40J\207\377"
   "\202\0\0\0\0\202\40J\207\377\2\40J\207E\40J\207\2\202\0\0\0\0\1\0\0\0"
   "\2\203\0\0\0\0\4\40J\2072\40J\207\377\276\322\352\377\40J\207\377\202"
   <data continues......>
   "\0\0\0\0\1\40J\207\1\204\0\0\0\0\1\40J\207\3\227\0\0\0\0\1\0\0\0\3\244"
};

I want to include the icons in some buttons, so I prepared the following series of statements:

GtkWidget *icon_flipH = gtk_image_new_from_pixbuf(gdk_pixbuf_from_pixdata(&pixdata_flipH, FALSE, NULL));
GtkWidget *icon_flipV = gtk_image_new_from_pixbuf(gdk_pixbuf_from_pixdata(&pixdata_flipV, FALSE, NULL)); 
// and so on...

In this way I'll add the image to the button with the function:

gtk_button_set_image(GTK_BUTTON(button_flipH), icon_flipH);

Well... The GCC compiler goes in error saying that "initializer element is not constant" at each line containing gdk_pixbuf_from_pixdata() function. I can't figure out why, because the function needs a const structure pointer and actually my structures are declared 'const'.

Am I forgetting something? Is it not the right way to include images into the code and create pixbufs? Any tutorial in this case?

Answer 1

Objects defined at file scope (like icon_flipH ) have static storage duration: their lifetime is the lifetime of the program and they are initialized before the startup of the program. You can only initialize objects with static storage duration with a constant expression (eg, 0 , 10 + 32 , or sizeof (int) ). The result of a function call is not a constant expression.

// File scope

GtkWidget *icon_flipH = NULL;   // OK, NULL is a constant expression  
GtkWidget *icon_flipV = foo();  // Not OK, foo is not a constant expression