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Adding to char Arrays via loops

Posted on 2004-08-21
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Last Modified: 2010-04-01
What I am trying to do is generate lists of files in folders and store them in a char array. However, I dont know how to add a filename on the next loop. How do you add things to a character array?

You cant do it like this:

char ch = new char[];

ch = "hi";

ch = ch + "hi"; // does not work

ch += "hi"; // does not work


I tried using strcat() but my program crashes whenver I use it.

Anyone?data2
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Question by:sint4x
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6 Comments
 
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Expert Comment

by:Axter
ID: 11862728
>>char ch = new char[];

The above should be the following:

char *ch = new char[123]; //Where 123 is the size of the array that you want
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Expert Comment

by:Axter
ID: 11862736
char *ch = new char[123];

strcpy(ch, "Hello ");
strcat(ch, "World");

cout << ch << endl;
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Author Comment

by:sint4x
ID: 11863891
Ahh, i see the only reason why it keeps crashing is because I didn't specify an array size.

Now how do I reset the size after I add things? (getting a directory list could be very large.)
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LVL 30

Accepted Solution

by:
Axter earned 125 total points
ID: 11864915
>>Ahh, i see the only reason why it keeps crashing is because I didn't specify an array size.

Also, because it was not being assign to a pointer.


>>Now how do I reset the size after I add things? (getting a directory list could be very large.)

I recommend you use a std::vector and an std::string for this requirement.
Example:

#include <vector>
#include <string>
#include <iostream>

std::vector<std::string> MyArrayOfFileNames;

//To add a name
MyArrayOfFileNames.push_back("SomeFileName");

//To referance a name

std::cout << MyArrayOfFileNames[0] << std::endl;

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Expert Comment

by:Axter
ID: 11864926
>>Now how do I reset the size after I add things? (getting a directory list could be very large.)

Otherwise, you would need to create an array of pointer, which would require that you have an idea of the quantity of file names you're going to store in advance.

Then you would have to assign space for each file name, and set it to an each array pointer item.
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LVL 3

Expert Comment

by:CmdrRickHunter
ID: 11876027
do you understand pointers?  If not, then this is going to be some black magic:

char* data = new char[256],
      * p = data; // "p" moves along in the "data" array
const char[] filename1 = "hello\n";
const char[] filename2 = "world\n";
strcpy(p, filename1); // put "hello\n" into p (into the data array)
p += strlen(filename1); // this is the pointer magic
strcpy(p, filename2);
p += strlen(filename2);


what the "p += strlen(theStringJustCopied)" does is move p forward in memory, so that it points to the character one after the last character you added.

just remember, even though p is a char*, dont delete it!!  All its doing is pointing to memory that got allocated as part of "data".  DELETE "data" NOT "p"!!!


if you really want to:

void AddToBuffer(char*& inP, const char* inNewString)  // if this doesn't work, try char &*
{
   strcpy(inP, inNewString);
   inP += strlen(inNewString);
}


then you can do
char* data = new char[1250];
char * p = data;
AddTobuffer(p, "Hello ");
AddToBuffer(p, "world");


the trick to that working is the "pass pointer by reference", which passes a char*, but does so by reference so that we can change what the pointer is pointing AT.
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