Solved

Simple CFile question

Posted on 2002-03-24
6
268 Views
Last Modified: 2013-11-20
When reading a file, I want to pick up a string after a series of reads of different structures.  However after reading in a string, the string that is read in contains garbage after it.  So then I found that after I created a temp character pointer initialized to a size of one and then read it in, it seemed to read the string correctly however it wont let me delete the string after a loop:

char* tempName;
for (y = 0; y < NUM_SAMPLES_ALLOWED; y++)
{
   if (lengthOfFileNames[y] > 0)
   {
      //When the following is initialized to the actual
      //  size of the string to read, the string is
      //  retrieved but has garbage after it
      //  example:   'c:\myfiles\myfile.doc@@@@@@'
      //  Initializing it to 0 or 1 seems to work for some
      //    unknown reason.  
      tempName = new char[1];
      savedFile.Read(tempName,sizeof(char)
           * lengthOfFileNames[y]);          
      filePaths[y] = tempName;

      //It crashes if I include the following line:
      //delete [] tempName;
   }
}


So now with this bizzare initialization of size 1 and a no delete line, it works but could someone tell me why??
Do I have a memory leak without that delete [] tempName?
0
Comment
Question by:c121hains
6 Comments
 
LVL 3

Accepted Solution

by:
GGRUNDY earned 100 total points
ID: 6892698
Hi,

savedFile.Read(tempName,sizeof(char)* lengthOfFileNames[y]);    

If lengthOfFileNames[y] had a value anything other than 1 then the above line will lead memory corruption.
If, say lengthOfFileNames[y] had a value of 100, then you would be reading 100 bytes of data into a memory area only one byte long (tempName), thereby creaming 99 bytes of unsuspecting innocent memory.

Plus you don't seem to be taking any steps to NULL terminate the filenames you read.

Cheers
0
 
LVL 6

Expert Comment

by:Triskelion
ID: 6892795
Why are you calling new and delete for one byte?
Even though it is technically an array, if you must use delete, remove the braces [].
This my have nothing (really) to do with your problem.
0
 
LVL 3

Expert Comment

by:job_s
ID: 6893358
why did u call delete [] U were allocated only one char

if u want to read a string U must allocate the size of bytes in the source string + 1 for the NULL termination.
Before reading the string call ZeroMemory or memset for clearing the buffer. Otherwise delete[] will crash becasue delete[] will look for the NULL char for finding the end of string.

0
 
LVL 4

Expert Comment

by:mblat
ID: 6900659
Running couple assumptions here:

Assuming you data strcuture looks like:

typedef struct
{
int   lengthOfFileNames;
char  filePaths[MAX_PATH];
} STRUCT;

then you declare var of this type like:
STRCUT s[NUM_SAMPLES_ALLOWED];

if so, your loop should look like

char* tempName;
for (y = 0; y < NUM_SAMPLES_ALLOWED; y++)
{
  if (lengthOfFileNames[y] > 0)
  {
     tempName = new char[lengthOfFileNames[y] + 1];
     memset(tempName,0,sizeof(char)*(lengthOfFileNames[y]+1);
     savedFile.Read(tempName,sizeof(char)*lengthOfFileNames[y]);          

     strcpy(filePaths[y],tempName);
     delete tempName;
  }
}
0

Featured Post

Is Your Active Directory as Secure as You Think?

More than 75% of all records are compromised because of the loss or theft of a privileged credential. Experts have been exploring Active Directory infrastructure to identify key threats and establish best practices for keeping data safe. Attend this month’s webinar to learn more.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Suggested Solutions

Introduction: Dialogs (2) modeless dialog and a worker thread.  Handling data shared between threads.  Recursive functions. Continuing from the tenth article about sudoku.   Last article we worked with a modal dialog to help maintain informat…
If you use Adobe Reader X it is possible you can't open OLE PDF documents in the standard. The reason is the 'save box mode' in adobe reader X. Many people think the protected Mode of adobe reader x is only to stop the write access. But this fe…
This video will show you how to get GIT to work in Eclipse.   It will walk you through how to install the EGit plugin in eclipse and how to checkout an existing repository.
Learn how to create flexible layouts using relative units in CSS.  New relative units added in CSS3 include vw(viewports width), vh(viewports height), vmin(minimum of viewports height and width), and vmax (maximum of viewports height and width).

920 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

17 Experts available now in Live!

Get 1:1 Help Now