C++ help

[redsox]

I am currently writing a program to read in certain values from a text document, modify the values, and output the answer onto the screen.

Here is the code that I found online with which I am reading the file.

char str[5];


	fstream file_op("d:20060914-152330.txt",ios::in);


	while(!file_op.eof())


		{


			  file_op.getline(str,5);


			  cout <<str;


		}		 file_op.close();


		cout <<endl;

Can someone please tell me what the 5 represents? I thought it represented the number of characters the program would read from the file, but I am not too sure about it. Here is the text document that I am trying to read.

38973.82499	0.77609	1392	1490	827	865	1709	1315	850	1398	1493	829	866	1712	1329	860	0	0	0	0	0	0	0


38973.82569	0.77436	1388	1485	824	861	1703	1308	842	1395	1486	825	862	1704	1326	857	0	0	0	0	0	0	0


38973.82638	0.77261	1379	1474	819	857	1695	1305	829	1386	1473	818	856	1693	1319	839	0	1	0	1	2	0	0


38973.82708	0.77085	1375	1467	816	854	1689	1301	815	1381	1468	816	854	1690	1317	826	0	0	0	0	1	0	0


38973.82777	0.76907	1369	1462	813	851	1684	1296	805	1376	1462	813	851	1684	1313	819	0	0	0	0	0	0	0


38973.82847	0.76728	1363	1456	810	848	1678	1294	803	1373	1457	811	848	1678	1309	815	0	0	0	0	0	0	0


38973.82916	0.76548	1363	1457	810	848	1677	1292	803	1370	1457	810	848	1678	1307	816	0	0	0	0	0	0	0


38973.82986	0.76366	1362	1457	810	847	1675	1290	810	1371	1458	811	847	1677	1306	823	0	0	0	0	0	0	0


38973.83055	0.76183	1361	1456	809	846	1673	1288	810	1368	1456	810	845	1673	1303	821	0	0	0	0	1	0	0


38973.83125	0.75998	1357	1451	807	844	1668	1284	802	1363	1451	807	843	1668	1300	814	0	0	0	0	0	0	0


38973.83194	0.75812	1348	1439	801	839	1660	1280	782	1354	1438	800	838	1659	1295	792	0	0	0	0	1	0	0


38973.83263	0.75625	1340	1430	797	834	1652	1274	772	1347	1430	796	834	1652	1290	785	0	1	0	0	0	0	0


38973.83333	0.75436	1337	1426	795	833	1649	1274	771	1344	1427	796	833	1651	1286	782	0	0	0	0	0	0	0


38973.83402	0.75246	1334	1424	794	830	1644	1267	773	1343	1425	794	831	1646	1283	785	0	0	0	0	0	0	0


38973.83472	0.75054	1331	1422	792	828	1640	1264	772	1338	1422	792	828	1641	1280	784	0	1	0	1	1	0	0


38973.83541	0.74861	1330	1422	792	828	1638	1261	773	1337	1422	792	828	1640	1278	785	0	0	0	0	1	0	0


38973.83611	0.74667	1323	1413	787	823	1631	1257	762	1330	1414	788	825	1633	1273	772	0	0	0	0	0	0	0


38973.83680	0.74472	1315	1403	782	819	1622	1251	751	1323	1405	783	820	1625	1268	761	0	0	0	0	0	0	0


38973.83750	0.74275	1305	1388	775	813	1612	1247	730	1312	1389	775	813	1613	1260	741	0	0	0	0	0	0	0


38973.83819	0.74076	1303	1386	774	812	1610	1244	726	1309	1386	774	812	1610	1258	737	0	0	0	0	0	0	0


38973.83888	0.73877	1298	1378	770	808	1603	1239	722	1306	1379	770	809	1605	1255	733	0	0	0	0	0	0	0


38973.83958	0.73675	1294	1373	768	806	1600	1238	717	1300	1374	768	807	1600	1251	727	0	0	0	0	1	0	0


38973.84027	0.73473	1291	1371	767	805	1596	1234	710	1296	1371	767	805	1595	1248	721	0	1	0	0	1	0	0


38973.84097	0.73269	1283	1361	762	800	1588	1230	700	1291	1362	762	800	1590	1245	710	0	0	0	0	0	0	0


38973.84166	0.73064	1279	1352	757	797	1582	1228	696	1284	1352	758	797	1583	1240	706	0	0	0	0	0	0	0


38973.84236	0.72858	1278	1353	757	796	1580	1224	702	1284	1351	757	796	1579	1239	713	0	1	0	0	1	0	0


38973.84305	0.72650	1282	1363	762	798	1584	1225	720	1290	1364	763	799	1585	1238	730	0	0	0	0	1	0	0


38973.84375	0.72441	1279	1361	761	797	1581	1222	712	1285	1361	760	796	1580	1236	722	0	1	0	0	1	0	0


38973.84444	0.72231	1273	1356	758	794	1575	1218	707	1281	1356	758	794	1575	1231	717	0	0	0	0	0	0	0


38973.84513	0.72019	1269	1352	756	791	1569	1213	702	1275	1352	756	791	1570	1224	711	0	0	0	0	0	0	0


38973.84583	0.71806	1262	1344	752	786	1560	1206	696	1267	1345	752	786	1561	1219	704	0	0	0	0	0	0	0


38973.84652	0.71592	1254	1334	746	782	1552	1201	685	1259	1335	747	782	1553	1211	692	0	0	0	0	0	0	0


38973.84722	0.71376	1246	1324	741	777	1542	1194	672	1252	1325	742	778	1543	1206	681	0	0	0	0	0	0	0

I want to take the values from the second and third column and use them to calculate a particular output. The output will be just one particular value. My question is how do I grab those two particular columns. I am assuming that I have to specify for the program to look for a space to differentiate between the two columns. But I am not sure as to how I can do that.

Any help would be very much appreciated. Thank you.

[Ghostrider]

You are right in your assumption that the "5" represents the number of characters. Check this site for some tips on cleaning up that code. I'm not entirely sure that you want to use a eof(). But if it works for you, go for it.

[redsox]

Thanks for the reply. I am a novice in programming, so basically I just go with what I find online. Also, what site are you referring to - this MVPMODS site?

Do you know how I can store just the two columns that I need for my calculations? It would be nice if the program would read the file and display the data but I am more interested in storing the said columns to a variable (maybe an array? not sure) and use that variable to make my changes.

Thank you for the help.

[Ghostrider]

Thanks for the reply. I am a novice in programming, so basically I just go with what I find online. Also, what site are you referring to - this MVPMODS site?

Do you know how I can store just the two columns that I need for my calculations? It would be nice if the program would read the file and display the data but I am more interested in storing the said columns to a variable (maybe an array? not sure) and use that variable to make my changes.

Thank you for the help.

Crap, I forgot to link the site in my previous post.

http://cboard.cprogramming.com/showthread.php?t=69403

It seems like that thread talks about something similar to what you are trying to do.

[ronmexico]

You can use a regex if you are willing to put it in this form 'the column info'

It's the simplest thing I thought of, but I'm sure I'll think of something if I have a moment to think about it, so off to lunch then.

[ronmexico]

Good news, I didn't get to lunch before I thought of something, since all your columns start in the same place on every line, you can start reading from a certain character # on a line (like read the 10th to 15th and then the 17th to the 22nd) and use that data.

[redsox]

Good news, I didn't get to lunch before I thought of something, since all your columns start in the same place on every line, you can start reading from a certain character # on a line (like read the 10th to 15th and then the 17th to the 22nd) and use that data.

Thanks a bunch for that. That is exactly what I am looking to do. Would I use the getline command to do that? You had mentioned that I could just read the 10th to 15th characters etc., but how would that work if I have more rows. At the moment, I have about 33 rows but other files could have more than 33 rows (more like 50 or even in the 100s).

Or does that not matter. I guess it really wouldn't matter how many rows I have since it will always be looking for the 10th to 15th characters and the 17th to 22nd characters on any row, correct? Thanks for the help.

@ Ghostrider - Thanks for the link. I will take a look at the link that you had provided me with. Take care.

[ronmexico]

Not too sure about the getline command question because I haven't done C++ in a while and I kinda don't like the API of it, so it will take me a bit to find it most probably. Secondly, it doesn't matter how many rows because what you should be doing anyways is looping it like so:

while(getline!=null)


{


	   getline


}

I looked at your code and found that the eof function does just that,t eh getline!=null so you can keep the eof loop.

[redsox]

Thank you. I will give it a try. Take care.

[ronmexico]

Thought of something much simpler.

substr(size_type pos, size_type n)


meaning


substr(place you start, how long)




Heres an example:


string str18 = "abcdefghi"


string str19 = str18.substr (6,2);


cout << str19 << endl; 


// prints out "gh"

initialize i to 0 or 1, 1 if line numbers start at 1 in C++ 0 if they start at 0.


while(!file_op.eof())


		{


			  file_op.getline(str,i);


			  cout <<str.substr(start point, how many chars);


			  i++


		}		 file_op.close();


		cout <<endl;




That's the code to get it to print out the substring for whatever you wanted it as.

[redsox]

Thank you very much. BTW, I would have to define my variable as a floating point variable correct (instead of a string variable)?

[ronmexico]

No, you can only take the substring of a string.

Also, since you are just printing the numbers, you don't need to make them anything but a string.

[redsox]

I am having some trouble getting this to work right. Here is my modified code based on your example.

ifstream indata; // indata is like cin


	char str[5000];


	fstream file_op("d:20060914-152330.txt",ios::in);






	char i=0;




		while(!file_op.eof())


		{


			  file_op.getline(str,i);


			  cout << str.substr (12,7);


			  i++;


		}		 file_op.close();


		cout <<endl;

I am getting the following error:

error C2228: left of '.substr' must have class/struct/union type


Error executing cl.exe.

I think this is due to the fact that I have defined str as a char but I am not able to say "string str=0;" - to initialize.

I have included the <string.h> header file. Is there anything more I need to add? Thank you.

[ronmexico]

I didn't notice the char [] before, why not just make it a string?

Heres some help on that subject if need be

http://www.mochima.com/tutorials/strings.html

[redsox]

Thats what I planned on doing but I wasn't able to define the string. Now I know that I had included the wrong header file.

Thanks for the link and for your help. I will post as I move along in this program.

[redsox]

I had modified my code to resemble this, but I am still not able to get it to work. I am not able to view anything on the screen. I just get a black command box.

Here is the modified code.

string str;


	ofstream myfile ("20060914-152330.txt");


	while(myfile.is_open())


		{


			cin >> str;


			  getline (cin,str);


			  cout <<str;


		}




	myfile.close();


	cout <<endl;

Thanks for anyone who can help me with this. Please keep in mind that I am novice at c++. I just know the very basic information and nothing more. Take care.

[ronmexico]

Well you only get stuff in the command prompt because you didn't write anything that would make it visual. You have to create GUI's n such for it to work with a screen of sorts. I've taken up learning Objective-C (a language commonly used for Mac Cocoa applications) and I don't know much about making GUI's because it is a similar style to VB.net GUI making.

cout prints to command line for the record.

[redsox]

Thank you very much for the reply.

I wouldn't have to create a GUI to just display some values in a command box correct?

I thought the "cout" command would print what ever you want to be printed on to the black command box that pops up when your run the code.

I was actually trying to debug and found out that it has to do with the way I am opening the file. I added the following code before:

ofstream myfile ("20060914-152330.txt");

and I was able to see "Just a test".

cout << "Just a test" << endl;

I am really not sure as to how can fix the problem. Thank you very for your help.

[ronmexico]

I'll look it up next time I get an internet connection, sometime hopefully within this week in Norway.

[redsox]

Thanks a lot for your help ronmexico. To give you an update. I was able to read in the whole file by using the following set of commands.

string str;


	ifstream myfile ("20060914-152330.txt");


	if (myfile.is_open())


	{


		while (! myfile.eof() )


		{


			getline (myfile,str);


			cout << str << endl;


		}




		myfile.close();


	}




	else cout << "Unable to open file";

And I was able to output the first column I need by using the following code:

cout <<str.substr(12,7) << endl;


			i++;

The final step I need to do is to take the values in the particular column I had read and store it so that I can make some changes. For example, I would like to take the inverse cosine of all the values in that particular column and display the acquired result. I would very much be thankful if someone could answer that final part for me. Take care.

[redsox]

I got it!

Thanks for all the help. I had to define another variable and use "myfile" to read and store the column data in a variable. I just used the following commands:

myfile >> column1 >> column2 >> column3;

As of this moment, everything seems to be working great. Hopefully the whole program will run smoothly. Take care.

[ronmexico]

Good job and good luck, I found wifi in some small wonderful town, which I was attracted to not because of the wifi, but the fact that it was 100 KM out of Alta, which means I have a short trip tommorow after a 900 KM drive. It looks good to me and nice coding if I may say so myself ;)

[redsox]

Sounds like you are having a nice road trip.

And thanks for all the help. Everything seems to be running smoothly now. Take care.