Question

I am working with a PTP (ISO 15740) library (manipulating camera settings via USB host) for the Arduino. It uses this constant, which appears to be some kind of hashtable array. The problem is I don’t know what it’s called, so I am not sure how to search for it online, and since I am not a seasoned C++ programmer I don’t know how to use it. How does this work?

const ValueTitle<VT_SHSPEED, VT_SHSPEED_TEXT_LEN> ShutterSpeedTitles[] PROGMEM =
{
{0x0c,  {'B','u','l','b',0} },
{0x10,  {' ','3','0','"',0} },
{0x13,  {' ','2','5','"',0} },
{0x14,  {' ','2','0','"',0} },
{0x15,  {' ','2','0','"',0} },
{0x18,  {' ','1','5','"',0} },
{0x1B,  {' ','1','3','"',0} },
{0x1C,  {' ','1','0','"',0} },
{0x1D,  {' ','1','0','"',0} },
{0x20,  {' ',' ','8','"',0} },
{0x23,  {' ',' ','6','"',0} },
{0x24,  {' ',' ','6','"',0} },
{0x25,  {' ',' ','5','"',0} },
{0x28,  {' ',' ','4','"',0} },
{0x2B,  {' ','3','"','2',0} },
{0x2C,  {' ',' ','3','"',0} },
{0x2D,  {' ','2','"','5',0} },
{0x30,  {' ',' ','2','"',0} },
{0x33,  {' ','1','"','6',0} },
{0x34,  {' ','1','"','5',0} },
{0x35,  {' ','1','"','3',0} },
{0x38,  {' ',' ','1','"',0} },
{0x3B,  {' ','0','"','8',0} },
{0x3C,  {' ','0','"','7',0} },
{0x3D,  {' ','0','"','6',0} },
{0x40,  {' ','0','"','5',0} },
{0x43,  {' ','0','"','4',0} },
{0x44,  {' ','0','"','3',0} },
{0x45,  {' ','0','"','3',0} },
{0x48,  {' ',' ',' ','4',0} },
{0x4B,  {' ',' ',' ','5',0} },
{0x4C,  {' ',' ',' ','6',0} },
{0x4D,  {' ',' ',' ','6',0} },
{0x50,  {' ',' ',' ','8',0} },
{0x53,  {' ',' ','1','0',0} },
{0x54,  {' ',' ','1','0',0} },
{0x55,  {' ',' ','1','3',0} },
{0x58,  {' ',' ','1','5',0} },
{0x5B,  {' ',' ','2','0',0} },
{0x5C,  {' ',' ','2','0',0} },
{0x5D,  {' ',' ','2','5',0} },
{0x60,  {' ',' ','3','0',0} },
{0x63,  {' ',' ','4','0',0} },
{0x64,  {' ',' ','4','5',0} },
{0x65,  {' ',' ','5','0',0} },
{0x68,  {' ',' ','6','0',0} },
{0x6B,  {' ',' ','8','0',0} },
{0x6C,  {' ',' ','9','0',0} },
{0x6D,  {' ','1','0','0',0} },
{0x70,  {' ','1','2','5',0} },
{0x73,  {' ','1','6','0',0} },
{0x74,  {' ','1','8','0',0} },
{0x75,  {' ','2','0','0',0} },
{0x78,  {' ','2','5','0',0} },
{0x7B,  {' ','3','2','0',0} },
{0x7C,  {' ','3','5','0',0} },
{0x7D,  {' ','4','0','0',0} },
{0x80,  {' ','5','0','0',0} },
{0x83,  {' ','6','4','0',0} },
{0x84,  {' ','7','5','0',0} },
{0x85,  {' ','8','0','0',0} },
{0x88,  {'1','0','0','0',0} },
{0x8B,  {'1','2','5','0',0} },
{0x8C,  {'1','5','0','0',0} },
{0x8D,  {'1','6','0','0',0} },
{0x90,  {'2','0','0','0',0} },
{0x93,  {'2','5','0','0',0} },
{0x94,  {'3','0','0','0',0} },
{0x95,  {'3','2','0','0',0} },
{0x98,  {'4','0','0','0',0} },
{0x9B,  {'5','0','0','0',0} },
{0x9C,  {'6','0','0','0',0} },
{0x9D,  {'6','4','0','0',0} },
{0xA0,  {'8','0','0','0',0} }
};

Essentially what I am looking for in the end is this. The hex values represent a shutter speed on the camera. The data to the right of the hex humber is the value of the shutter speed if it were visible on the camera display in single character terms. (I guess this could be called a matrix?). I want to plug in my device, and set an exposure on the camera. We’ll say a one second exposure which is represented by the hex value “0x38”. This is a starting point reference.

I want to take five pictures. One of them is “0x38” while the two of the other four are the two exposures before this one, and the other two are the two exposures after this one. So I want to put all five hex values in an array in order so it’d find “0x38” and then search two below, and then find one below, and then the reference, then one above and then two above.

Answer 1

It is an array initializer:

Example:

int  val[] = {1, 2, 3, 4}; // initializes an array of ints.

If you have struct the same syntax works.

struct X
{
    int x;
    int y;
};

X   valX[] = { {1,2}, {3,4}, {5,6}}; // initializes an array of X
                                     // first X is {1,2}
                                     // second X is {3,4}
                                     // etc

In your case the structure is a:

ValueTitle<VT_SHSPEED, VT_SHSPEED_TEXT_LEN>

But the concept is the same;