Compiling existing C programs in VS.NET 2005

Question

sadhramani 0 Newbie Poster

14 Years Ago

int do_openFile(void)
{
   char *p ;                  /* pointer to outFileName */
   char *m ;                  /* pointer to report date */
   char *mon;                 /* month number in report date */



   /* get output file name   */
  m = pk->CNCRptdate;
  m += 2;
  strncpy(mon, m, 2);

  p = outFileName ;

  strcpy(p, pi->CNDExtransit);  
  p += 5;
  strcpy(p, monTab[atoi(mon)]);           
  p += 3;
  strcpy(p, ".");                         
  p += 1;
  strcpy(p, "TXT");

  /* Open a new file for writing, if file exists, its contents are destroyed
   */
 if ((outfile = fopen(outFileName, "w")) == NULL)
     {
	printf ("                                           \r");
	printf ("fopen failed\n");
	printf ("Please hit 'PRINT SCREEN' and then hit ENTER to abort...\n");
	getch();
	return (0);
     };
}

Issue: When the control hits the first strncpy() function, it throws "Unhandled exception at 0x00401acd in ICRSEX2B.exe: 0xC0000005: Access violation writing location 0x0040258f."

Pls let me know if any other information is required.

c++

Edited 14 Years Ago by kvprajapati because: Added [code] tags. Encase your code in: [code] and [/code] tags.

3 Contributors
6 Replies
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Latest Post 14 Years Ago Latest Post by Narue

Narue 5,707 Bad Cop

14 Years Ago

>strncpy(mon, m, 2);
Where does mon point?

Narue 5,707 Bad Cop

14 Years Ago

>mon is a character pointer variable.
I didn't ask you what it was, I asked you where it points. My question is an answer to your question. When you can answer my question satisfactorily, you'll learn what your problem is.

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sadhramani 0 Newbie Poster · Answer 1 · 2010-02-01T20:09:30+00:00

char *mon;
mon is a character pointer variable.
Is there any problem with the declaration?

Ancient Dragon 5,243 Achieved Level 70 Team Colleague Featured Poster · Answer 2 · 2010-02-01T20:57:19+00:00

char *mon;
mon is a character pointer variable.
Is there any problem with the declaration?

strncpy() does not allocate memory for the destination address, that has to be done by the calling function. So you might want to declare it like this: char mon[255] = {0}; . That allocated enough memory to store 255 characters in that buffer. Change that number to whatever you think will be needed. It will also initialize each of the bytes to '\0';

And my attempt to get the OP to actually use his brain is now wasted effort. Arigatou gozaimashita.

sadhramani 0 Newbie Poster · Answer 3 · 2010-02-01T22:55:47+00:00

Narue, I forgot to you tell you one important info. I am totally new to C/C++/VC++. Basically I am a .NET programmer. I am being forced to do this job. But anyway it is a good learning for me.

Might be in your next reply you can be more descriptive considering me as a beginner

Narue 5,707 Bad Cop Team Colleague · Answer 4 · 2010-02-02T05:40:46+00:00

>I am totally new to C/C++/VC++.
Yes, I figured that out on my own.

>Might be in your next reply you can be more descriptive considering me as a beginner
I pointed out your exact error and described it in such a way that a little research on your part would produce a solution. Even a .NET programmer can figure out what to do with such a detailed hint. ;)

Here's a bigger hint: Uninitialized pointers are not pointers to infinite memory. They're pointers to random addresses. I'm sure you can imagine the havoc wreaked by using random memory blocks as if you own them, and you have at least one real world example now.