how to declare a constant variable from a static variable in C?

Question

I want to get a constant variable from this static variable.

#define video_mode_count 12
static freenect_frame_mode supported_video_modes[video_mode_count] = {
    // reserved, resolution, format, bytes, width, height, data_bits_per_pixel, padding_bits_per_pixel, framerate, is_valid
    {MAKE_RESERVED(FREENECT_RESOLUTION_HIGH,   FREENECT_VIDEO_RGB), FREENECT_RESOLUTION_HIGH, {FREENECT_VIDEO_RGB}, 1280*1024*3, 1280, 1024, 24, 0, 10, 1 },
    {MAKE_RESERVED(FREENECT_RESOLUTION_MEDIUM, FREENECT_VIDEO_RGB), FREENECT_RESOLUTION_MEDIUM, {FREENECT_VIDEO_RGB}, 640*480*3, 640,  480, 24, 0, 30, 1 },

    {MAKE_RESERVED(FREENECT_RESOLUTION_HIGH,   FREENECT_VIDEO_BAYER), FREENECT_RESOLUTION_HIGH, {FREENECT_VIDEO_BAYER}, 1280*1024, 1280, 1024, 8, 0, 10, 1 },
    {MAKE_RESERVED(FREENECT_RESOLUTION_MEDIUM, FREENECT_VIDEO_BAYER), FREENECT_RESOLUTION_MEDIUM, {FREENECT_VIDEO_BAYER}, 640*480, 640, 480, 8, 0, 30, 1 },

    {MAKE_RESERVED(FREENECT_RESOLUTION_HIGH,   FREENECT_VIDEO_IR_8BIT), FREENECT_RESOLUTION_HIGH, {FREENECT_VIDEO_IR_8BIT}, 1280*1024, 1280, 1024, 8, 0, 10, 1 },
    {MAKE_RESERVED(FREENECT_RESOLUTION_MEDIUM, FREENECT_VIDEO_IR_8BIT), FREENECT_RESOLUTION_MEDIUM, {FREENECT_VIDEO_IR_8BIT}, 640*488, 640, 488, 8, 0, 30, 1 },

    {MAKE_RESERVED(FREENECT_RESOLUTION_HIGH,   FREENECT_VIDEO_IR_10BIT), FREENECT_RESOLUTION_HIGH, {FREENECT_VIDEO_IR_10BIT}, 1280*1024*2, 1280, 1024, 10, 6, 10, 1 },
    {MAKE_RESERVED(FREENECT_RESOLUTION_MEDIUM, FREENECT_VIDEO_IR_10BIT), FREENECT_RESOLUTION_MEDIUM, {FREENECT_VIDEO_IR_10BIT}, 640*488*2, 640, 488, 10, 6, 30, 1 },

    {MAKE_RESERVED(FREENECT_RESOLUTION_HIGH,   FREENECT_VIDEO_IR_10BIT_PACKED), FREENECT_RESOLUTION_HIGH, {FREENECT_VIDEO_IR_10BIT_PACKED}, 1280*1024*10/8, 1280, 1024, 10, 0, 10, 1 },
    {MAKE_RESERVED(FREENECT_RESOLUTION_MEDIUM, FREENECT_VIDEO_IR_10BIT_PACKED), FREENECT_RESOLUTION_MEDIUM, {FREENECT_VIDEO_IR_10BIT_PACKED}, 640*488*10/8, 640, 488, 10, 0, 30, 1 },

    {MAKE_RESERVED(FREENECT_RESOLUTION_MEDIUM, FREENECT_VIDEO_YUV_RGB), FREENECT_RESOLUTION_MEDIUM, {FREENECT_VIDEO_YUV_RGB}, 640*480*3, 640, 480, 24, 0, 15, 1 },

    {MAKE_RESERVED(FREENECT_RESOLUTION_MEDIUM, FREENECT_VIDEO_YUV_RAW), FREENECT_RESOLUTION_MEDIUM, {FREENECT_VIDEO_YUV_RAW}, 640*480*2, 640, 480, 16, 0, 15, 1 },};

Now I need to write something

const FREENECT_VIDEO_RGB = [ An instance in the type of  freenect_frame_mode ]

How to declare a const var in that format?

The original codes from:

https://github.com/OpenKinect/libfreenect/blob/master/src/cameras.c#L42

And I need to pass a const var freenect_frame_mode into this, and see if it returns -1 or not:

https://github.com/OpenKinect/libfreenect/blob/master/src/cameras.c#L1152

int freenect_set_video_mode(freenect_device* dev, const freenect_frame_mode mode)
{
freenect_context *ctx = dev->parent;
if (dev->video.running) {
    FN_ERROR("Tried to set video mode while stream is active\n");
    return -1;
}
// Verify that the mode passed in is actually in the supported mode list
int found = 0;
int i;
for(i = 0 ; i < video_mode_count; i++) {
    if (supported_video_modes[i].reserved == mode.reserved) {
        found = 1;
        break;
    }
}
if (!found) {
    FN_ERROR("freenect_set_video_mode: freenect_frame_mode provided is invalid\n");
    return -1;
}

freenect_resolution res = RESERVED_TO_RESOLUTION(mode.reserved);
freenect_video_format fmt = (freenect_video_format)RESERVED_TO_FORMAT(mode.reserved);
dev->video_format = fmt;
dev->video_resolution = res;
// Now that we've changed video format and resolution, we need to update
// registration tables.
freenect_fetch_reg_info(dev);
return 0;

}

I am just stuck with using the function now.

Thanks!

A constant variable is definitelly not variable.... :) What about const static ... ??? — Luis Colorado
– Luis Colorado, Commented Sep 2, 2015 at 10:49

Chris Beck · Accepted Answer · 2015-08-31 17:57:41Z

3

Well, if you want to get an element of an array, you can use the standard syntax array[index].

const freenect_frame_mode FREENECT_VIDEO_RGB = supported_video_modes[5];

for example.

You need to show more code, i.e. the definitions of these symbols, if you want more info.

answered Aug 31, 2015 at 17:57

Chris Beck

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2 Comments

dotslash Over a year ago

The post was re-edited. I use the codes above it reported:

src/input/Freenect.cc:88:27: error: ‘const freenect_frame_mode FREENECT_VIDEO_RGB’ redeclared as different kind of symbol  const freenect_frame_mode FREENECT_VIDEO_RGB = supported_video_modes[5];

dotslash Over a year ago

well. I have fixed this problem. The error I got here is because that the var FREENECT_VIDEO_RGB was declared twice. I renamed the var name, and it works! Thank you, Chris Beck!

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