LookUp table Implementation in Qt

[rex]

Hello friends i have a doubt.. i am working on a Qt based application where i show some temperature data. I have a look up table where i save a temperature value to the db for a decimal value.. Right now i have the decimal value data into a QString which i am comparing with the decimal value and appending the equivalent Temperature value into a QVector which i am saving into the database.

if(str=="387")
	{
		temperaturedata.append("0");
	}else if(str=="414")
	{
		temperaturedata.append("10");
	}else if(str=="441")
	{
		temperaturedata.append("20");
	}else if(str=="469")
	{
		temperaturedata.append("30");
	}else if(str=="497")
	{
		temperaturedata.append("40");
	}else if(str=="525")
	{
		temperaturedata.append("50");
	}
     // And for all the other values also
.
.
.

if(str=="387")
	{
		temperaturedata.append("0");
	}else if(str=="414")
	{
		temperaturedata.append("10");
	}else if(str=="441")
	{
		temperaturedata.append("20");
	}else if(str=="469")
	{
		temperaturedata.append("30");
	}else if(str=="497")
	{
		temperaturedata.append("40");
	}else if(str=="525")
	{
		temperaturedata.append("50");
	}
     // And for all the other values also
.
.
.

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I wanted to know if there was a better way of handling a look up table, i have too many if else statements .. how could i handle this better..

This is how the look up table is.

Temperature Decimal
-40	289
-39	292
-38	294
-37	296
-36	299
-35	301
-34	303
-33	306
-32	308
-31	311
-30	313
-29	315
-28	318
-27	320
-26	323
-25	325
-24	328
-23	330
-22	333
-21	335
-20	337
-19	340
-18	342
-17	345
-16	347
-15	350
-14	352
-13	355
-12	358
-11	360
-10	363
-9	365
-8	368
-7	370
-6	373
-5	375
-4	378
-3	381
-2	383
-1	386
0	388
1	391
2	394
3	396
4	399
5	401
6	404
7	407
8	409
9	412
10	415
11	417
12	420
13	423
14	425
15	428
16	431
17	433
18	436
19	439
20	441
21	444
22	447
23	449
24	452
25	455
26	458
27	460
28	463
29	466
30	469
31	471
32	474
33	477
34	480
35	483
36	485
37	488
38	491
39	494
40	497
41	499
42	502
43	505
44	508
45	511
46	514
47	516
48	519
49	522
50	525

Temperature Decimal
-40	289
-39	292
-38	294
-37	296
-36	299
-35	301
-34	303
-33	306
-32	308
-31	311
-30	313
-29	315
-28	318
-27	320
-26	323
-25	325
-24	328
-23	330
-22	333
-21	335
-20	337
-19	340
-18	342
-17	345
-16	347
-15	350
-14	352
-13	355
-12	358
-11	360
-10	363
-9	365
-8	368
-7	370
-6	373
-5	375
-4	378
-3	381
-2	383
-1	386
0	388
1	391
2	394
3	396
4	399
5	401
6	404
7	407
8	409
9	412
10	415
11	417
12	420
13	423
14	425
15	428
16	431
17	433
18	436
19	439
20	441
21	444
22	447
23	449
24	452
25	455
26	458
27	460
28	463
29	466
30	469
31	471
32	474
33	477
34	480
35	483
36	485
37	488
38	491
39	494
40	497
41	499
42	502
43	505
44	508
45	511
46	514
47	516
48	519
49	522
50	525

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looking for some help.

Thank you

[Stef]

Instead of using all the else if statements did you consider using a QMap which seems perfect for these lookups.

[stampede]

Take a look at QHash, you can create a hash table mapping Decimal <-> temperature values, and instead of "if-else" statements simply call:

// _hash contains your Decimal <-> temperature table
if( _hash.contains(str) ){
    temperatureData.append( _hash.value(str) )
}

// _hash contains your Decimal <-> temperature table
if( _hash.contains(str) ){
    temperatureData.append( _hash.value(str) )
}

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----
Edit: looks like Stef was faster

[rex]

Hello thank you for the response. I did look at QMap but could't figure out how i should be doing it.. Din't find any example. Can you pls show a small example.

i will try your method also stampede thank you so much for the example code.

regards

[stampede]

Have you looked at the examples in QMap documentation ?
You just have to store values from your temperature table in such container ( initialize it once somewhere in the program ).

[Stef]

It's not that hard really. First you populate the lookup table with all keys and values. Then if you want to use it you just ask for the key of a specific value.

QMap<QString, QString> lookupTable;
 
    // Populate lookup table
    lookupTable.insert("-40", "289");
    lookupTable.insert("-39", "292");
    lookupTable.insert("-38", "294");
    lookupTable.insert("-37", "296");
    lookupTable.insert("-36", "299");
    lookupTable.insert("-35", "301");    
    // ... And so on
 
    // Use it
    temperaturedata.append(lookupTable.value(str));

QMap<QString, QString> lookupTable;
    
    // Populate lookup table
    lookupTable.insert("-40", "289");
    lookupTable.insert("-39", "292");
    lookupTable.insert("-38", "294");
    lookupTable.insert("-37", "296");
    lookupTable.insert("-36", "299");
    lookupTable.insert("-35", "301");    
    // ... And so on
    
    // Use it
    temperaturedata.append(lookupTable.value(str));

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[wysota]

QHash<int,int> lookUp;
lookup[-40] = 289;
lookup[-39] = 292;
// etc.

QHash<int,int> lookUp;
lookup[-40] = 289;
lookup[-39] = 292;
// etc.

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or using a static C array:

int valueFor(int v) {
  static int lookup[] = { 289, 292, 294, ... };
  return lookup[v+40];
}

int valueFor(int v) {
  static int lookup[] = { 289, 292, 294, ... };
  return lookup[v+40];
}

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[rex]

thanks a lot i will do it now.. You made it look so easy.