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Problem with Character Arrays

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Join Date: Jul 2005

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lyndonp

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Problem with Character Arrays

Jul 24th, 2005

I am not an expert C/C++ programmer, and am having a bit of a problem on a school assignment. The assignment is to build a text file based database. The program has to read a schema file containing information about the individual tables (table name, filename, data field name, type, and length). Then it must be able to read the data files and do operations on the tables.

A line from the schema file looks like this (it may wrap):

customer,customer.txt,customer_name,C,15,customer_street,C,15,customer_city,C,15:

A comma seperates the information and a colon terminates the line.

I created two structs that will hold the common data and also up to 10 sets of column data. The structs are shown below.
// Create a struct for the data elements
struct dataField
{
char fieldName[15];
char fieldType[1];
char fieldLen[2];
};

// Create class for a line describing one table schema limited to 10 data elements
struct schema
{
char tableName[15];
char fileName[15];
int fieldsUsed;
dataField data[10];
};

Without posting a large amount of code, I can get the text file read in and display the contents of the individual dataField element (such as fieldName) right after I load them. However, when I try to read the individual dataField.fieldName element any time after loading the next element, I get run together data like

customer_name C15customer_streetC15customer_city C15

Any ideas on why it doesn't seem to give me just the data I loaded? I am using a Microsoft VC++ environment to write a command line program.

Thanks.

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Join Date: Feb 2005

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winbatch

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Re: Problem with Character Arrays

Jul 24th, 2005

How are you printing out the columns? If you are using any functions that assume they are null terminated and you are not terminating them then you will get strange behavior...

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Sauce

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Re: Problem with Character Arrays

Jul 24th, 2005

Why not post the code that you are using to read in and display. Also make sure you are copying over and not overwriting the null terminator at the end of your char arrays. If you want to just test to see if you are, try strcat-ing a '\0' to the end of your char or manually put it in the last spot using its index value of each array. My guess is null terminator problem, see it often with new programmers.

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lyndonp

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Re: Problem with Character Arrays

Jul 25th, 2005

Sorry guys - I didn't want to post more code than I needed. I really figured that I must be doing something wrong with the struct declarations that cause a read of one dataField element to overrun the 15 character length. Here is the snippet of code that reads in from the CSV and writes to the struct.

Struct definations:

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 C++ Syntax (Toggle Plain Text) 
struct dataField
{
	char fieldName[15];
	char fieldType[1];
	char fieldLen[2]; 
};
 
struct schema 
{
	char tableName[15]; 
	char fileName[15];
	int fieldsUsed;
	struct dataField data[10];
};
 
schema schemaArray[10];
 
 
for (forvar = 0;forvar < 15; forvar++) nextWord[forvar]=' '; // clears nextWord[15] character variable
kk=0; // Resets nextWord counter
ii++; // Skip past comma (delimiter)
do 
{
	nextChar[1] = schemaLine[ii++];// Reads next character in schemaLine 
	nextWord[kk++] =  nextChar[1]; // Concats next character to the word
}
while (schemaLine[ii] != eOL && schemaLine[ii] != delim); // reads until eol or delimiter is reached
cout << nextWord << endl;// This correctly shows the expected data read in
strcpy (schemaArray[arrayLine].data[dataFieldNum].fieldName, nextWord);// loads data in schema array
cout << schemaArray[arrayLine].data[dataFieldNum].fieldName << endl; // this correctly shows data as well
struct dataField
{
	char fieldName[15];
	char fieldType[1];
	char fieldLen[2]; 
};

struct schema 
{
	char tableName[15]; 
	char fileName[15];
	int fieldsUsed;
	struct dataField data[10];
};

schema schemaArray[10];


for (forvar = 0;forvar < 15; forvar++) nextWord[forvar]=' '; // clears nextWord[15] character variable
kk=0; // Resets nextWord counter
ii++; // Skip past comma (delimiter)
do 
{
	nextChar[1] = schemaLine[ii++];// Reads next character in schemaLine 
	nextWord[kk++] =  nextChar[1]; // Concats next character to the word
}
while (schemaLine[ii] != eOL && schemaLine[ii] != delim); // reads until eol or delimiter is reached
cout << nextWord << endl;// This correctly shows the expected data read in
strcpy (schemaArray[arrayLine].data[dataFieldNum].fieldName, nextWord);// loads data in schema array
cout << schemaArray[arrayLine].data[dataFieldNum].fieldName << endl; // this correctly shows data as well

Once everything is loaded, this code should recall the contents of the same element.

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 C++ Syntax (Toggle Plain Text) 
int fn=0,al=0;
for (al=0;al<6;al++)
{
cout << schemaArray[al].tableName << " " << schemaArray[al].fileName << " " << schemaArray[al].fieldsUsed << " " << endl; // correctly displays table name and file name data from the schema struct
	for (fn=0; fn<3;fn++)
	{
cout << schemaArray[al].data[fn].fieldName; // displays customer_name  C15customer_streetC15customer_city  C15 - should display customer_name
cout << schemaArray[al].data[fn].fieldType; // displays C15customer_streetC15customer_city  C15 - should display C
cout << schemaArray[al].data[fn].fieldLen; //displays15customer_streetC15customer_city  C15 - should display 15
	}
 
}
int fn=0,al=0;
for (al=0;al<6;al++)
{
cout << schemaArray[al].tableName << " " << schemaArray[al].fileName << " " << schemaArray[al].fieldsUsed << " " << endl; // correctly displays table name and file name data from the schema struct
	for (fn=0; fn<3;fn++)
	{
cout << schemaArray[al].data[fn].fieldName; // displays customer_name  C15customer_streetC15customer_city  C15 - should display customer_name
cout << schemaArray[al].data[fn].fieldType; // displays C15customer_streetC15customer_city  C15 - should display C
cout << schemaArray[al].data[fn].fieldLen; //displays15customer_streetC15customer_city  C15 - should display 15
	}

}

The incorrect display is shown as comments on the last cout lines. As I mentioned earlier, I think that during the retrieval of the date, my mechanism is overrunning what should be the bonds of the dataField struct, but I can't figure out why.

Thanks.

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Join Date: Feb 2005

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winbatch

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Re: Problem with Character Arrays

Jul 25th, 2005

You can't print it out like that...cout looks for the null terminator.

If you want, increase the length of each member of the struct, then put a '\0' in the last character, then print it out.

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lyndonp

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Newbie Poster

Re: Problem with Character Arrays

Jul 28th, 2005

All,

Thanks for the great help - it was the null terminator that was causing the problem. Another newbie (me) gets bit by a simple problem, but you guys are great. Thanks again.

Lyndon