C / C++ / MFC

29-Jun-06 10:06

Hi everyone! Big Grin | :-D

Here I go again...;)
I'm writing a simple win32 console program.
so, I'm trying to open a text file that has the following in it:
0x00
0x01
0x02
0x03
0x04
0x05
0x06
0x07

What I want to do is open the file then get the data and stick it into an array of CString or whatever. i.e. data[0] = 0x0, data[1] = 0x1, etc.
Here is my code:

<br />
#include "stdafx.h"<br />
<br />
int _tmain(int argc, _TCHAR* argv[])<br />
{<br />
	char *data[200];<br />
	FILE *fpread;<br />
	int i = 0;<br />
	<br />
	if ( (fpread = fopen("data.txt", "r")) == NULL )<br />
	{<br />
		printf("Cannot open file for reading. \n");<br />
		return -1;<br />
	}<br />
<br />
        //initialize data<br />
	for ( int a = 0; a < 200; a++ )<br />
	{<br />
		data[a] = "q";<br />
	}<br />
<br />
	while( (feof(fpread) == 0 || ferror(fpread) == 0) )<br />
	{<br />
		fscanf(fpread, "%s", &data[i]); <- problem is here... i think<br />
		printf( "data = %s \n", data[i]);<br />
		i++;<br />
	}<br />
<br />
	if (feof(fpread) != 0)<br />
	{<br />
		printf("EOF\n");<br />
	}<br />
	else if (ferror(fpread) != 0)<br />
	{<br />
		printf("error!\n");<br />
	}<br />
<br />
	return 0;<br />
}<br />

When I run my code I get:
Unhandled exception at 0x0059f89f in testFileOpen.exe: 0xC0000005: Access violation reading location 0x30307830.

then it opens up the file: output.h and says that it has a problem with line 1646.

please explain.... Confused | :confused:

Kitty5

David Crow29-Jun-06 10:16

29-Jun-06 10:16

kitty5 wrote:
data[a] = "q";

You must allocate memory for data[a] before you can assign anything to it. Consider:

for (int a = 0; a < 200; a++)
{
    data[a] = new char[5]; // room for 0x## plus a terminating \0 character
    
    data[a][0] = 'q';
    data[a][1] = '\0';
    // or
    strcpy(data[a], "q");
}

Now the fscanf() statement, sans the &, should be fine (although initialization is not necessary).

kitty5 wrote:
while( (feof(fpread) == 0 || ferror(fpread) == 0) )

Use && instead.

"The largest fire starts but with the smallest spark." - David Crow

"Judge not by the eye but by the heart." - Native American Proverb

kitty529-Jun-06 10:25

29-Jun-06 10:25

<br />
<blockquote class="FQ"><div class="FQA">DavidCrow wrote:</div>You must allocate memory for data[a] before you can assign anything to it. Consider:<br />
<br />
<br />
for (int a = 0; a < 200; a++)<br />
{    <br />
data[a] = new char[5]; <br />
// room for 0x## plus a terminating \0 character        <br />
data[a][0] = 'q';    <br />
data[a][1] = '\0';    <br />
// or    <br />
strcpy(data[a], "q");<br />
}</blockquote><br />
<br />

I've also added the above code. However, I'm still getting the same error.

Kitty5

David Crow29-Jun-06 11:32

29-Jun-06 11:32

kitty5 wrote:
I've also added the above code. However, I'm still getting the same error.

But did you change the fscanf() statement, too?

"The largest fire starts but with the smallest spark." - David Crow

"Judge not by the eye but by the heart." - Native American Proverb

kitty529-Jun-06 11:37

29-Jun-06 11:37

yes

Kitty5

David Crow30-Jun-06 2:14

Re: file manipulation with fopen(), fscanf() [modified]

30-Jun-06 2:14

Strange. It worked fine for me with only those two changes.

void main( void )
{
    char *data[200];
    FILE *pFile;
    int i = 0;
 
    pFile = fopen("c:\\data.txt", "r");
    if (pFile != NULL )
    {
        for (int a = 0; a < 200; a++ )
            data[a] = new char[5];
 
        while ((feof(pFile) == 0 && ferror(pFile) == 0))
        {
            fscanf(pFile, "%s", data[i]);
            printf("data = %s \n", data[i]);
            i++;
        }
 
        fclose(pFile);
    }
}

"The largest fire starts but with the smallest spark." - David Crow

"Judge not by the eye but by the heart." - Native American Proverb

Zac Howland29-Jun-06 10:32

29-Jun-06 10:32

You actually have a couple problems:

kitty5 wrote:
//initialize data
for ( int a = 0; a < 200; a++ )
{
data[a] = "q";
}

Besides being inefficient, this is actually buggy. The reason is simple: You have an array of 200 unallocated strings. You are marching through all 200 and setting each one to "q\0". Since there is no memory allocated for these pointers ... you are writing in random places (NOT GOOD!).

kitty5 wrote:
fscanf(fpread, "%s", &data[i]); <- problem is here... i think

Don't use %s with scanf functions. In most cases, it won't do what you hope it will. Instead, use fread, or fgetc. A slightly better solution would be to read in the entire buffer at once (decreasing your harddrive accesses):

int _tmain(int argc, _TCHAR* argv[])
{
	char *data[200] = {0};	// initialize it here
	char* buffer = NULL;		// buffer for file
	FILE *fpread;
	int i = 0;

	if ((fpread = fopen("data.txt", "r")) == NULL)
	{
		printf("Cannot open file for reading. \n");
		return -1;
	}

	if (0 != fseek(fpread, 0, SEEK_END))
	{
		printf("Cannot seek end of file.\n");
		fclose(fpread);
		return -1;
	}

	size_t fileSize = ftell(fpread);
	if (0 != fseek(fpread, 0, SEEK_SET))
	{
		printf("Failed to seek beginning of file.\n");
		fclose(fpread);
		return -1;
	}

	buffer = new char[fileSize + 1];
	memset(buffer, 0, fileSize + 1);
	if (fileSize != fread(buffer, sizeof(char), fileSize, fpread))
	{
		printf("Failed to read file.\n");
		fclose(fpread);
		delete [] buffer;
		buffer = NULL;
		return -1;
	}

	// parse buffer here

	delete [] buffer;
	buffer = NULL;
	return 0;
}

If you decide to become a software engineer, you are signing up to have a 1/2" piece of silicon tell you exactly how stupid you really are for 8 hours a day, 5 days a week

Zac

-- modified at 16:33 Thursday 29th June, 2006

kitty529-Jun-06 10:55

29-Jun-06 10:55

Zac Howland wrote:
if (fileSize != fread(buffer, sizeof(char), fileSize, fpread))
{
printf("Failed to read file.\n");
fclose(fpread);
delete [] buffer;
buffer = NULL;
return -1;
}

Does the file need to be written in a special format?
I created it using notepad and saved it as: data.txt

When I try your code I get: Failed to read file.
This means that the number of items actually read (this is wha fread() returns) is not = to the fileSize.
This is true. So I don't understand why we're comparing the fileSize fo the number of items being read....

Kitty5

Zac Howland29-Jun-06 11:06

29-Jun-06 11:06

fileSize is the number of bytes in the file. You can place a breakpoint at that line to see what value is actually being returned and take a look at the contents of the buffer. However, the return value should be equal to fileSize if read completely. fread returns the number of "items" (which in this case is the same as the number of bytes) it reads.

You can read/write it in any format. However, in this case, you are trying to read a text file, so you will want to specify that in the fopen call.

If you decide to become a software engineer, you are signing up to have a 1/2" piece of silicon tell you exactly how stupid you really are for 8 hours a day, 5 days a week

Zac

kitty529-Jun-06 11:19

29-Jun-06 11:19

size_t size;<br />
	size = fread(buffer, sizeof(char), fileSize, fpread);<br />
	printf("fileSize = %d\n", fileSize);<br />
	printf("fread() = %d\n", size);

fileSize is = 96
fread() spits out = 80 items read.
the file is:
0x00
0x01
0x02
0x03
0x04
0x05
0x06
0x07
0x08
0x09
0x0a
0x0b
0x0c
0x0d
0x0e
0x0f

I understand where 80 comes from... there are 80 total characters including the \n.

Kitty5

Zac Howland29-Jun-06 15:57

Re: file manipulation with fopen(), fscanf() [modified]

29-Jun-06 15:57

The extra 16 characters are coming from the \r's that are attached to the \n's. If you want, you can just ignore the check for the size and use the buffer as is. There is a way to tell the f-functions to read \r's as well, but I can't remember how off the top of my head.

If you decide to become a software engineer, you are signing up to have a 1/2" piece of silicon tell you exactly how stupid you really are for 8 hours a day, 5 days a week

Zac

kitty529-Jun-06 11:55

29-Jun-06 11:55

int i = 0;
data[i] = strtok( buffer, " " );
printf("data[%d] = %s\n", i, data[i]);
do
{
i++;
data[i] = strtok( NULL, " " );
printf("data[%d] = %s\n", i, data[i]);
}while(data[i] && i<200);

how does one get strtok() to ignore a newline character?

Kitty5

-- modified at 17:59 Thursday 29th June, 2006

Zac Howland29-Jun-06 15:59

29-Jun-06 15:59

One way is to do a strtok on the '\n' character itself, which will give you a set of 0xXX strings.

If you decide to become a software engineer, you are signing up to have a 1/2" piece of silicon tell you exactly how stupid you really are for 8 hours a day, 5 days a week

Zac

Static Variables [modified]

Stephen Hewitt29-Jun-06 18:01

Stephen Hewitt

29-Jun-06 18:01

Here's how I would do it:
-------------------------

#include <iostream>
#include <fstream>
#include <string>
#include <vector>
#include <iterator>
#include <algorithm>

int main(int argc, char* argv[])
{
using namespace std;

// Open the file for reading.
ifstream ifs("C:\\a.txt");
if (!ifs)
{
cerr << "Unable to open file" << endl;
return 1;
}

// Read in the contents of the file.
typedef string type_t; // You can change the type of the data here.
typedef vector<type_t> container_t; // The collection we use to store the data we read.
container_t FileContents;
copy(
istream_iterator<type_t>(ifs), istream_iterator<type_t>(),
back_inserter(FileContents)
);

// Write the contents of the container to the console.
copy(
FileContents.begin(), FileContents.end(),
ostream_iterator<type_t>(cout, "\n")
);

return 0;
}

-------------------------

Changing a single line as follows reads and stores the data as ints instead or strings:
typedef int type_t; // You can change the type of the data here.

Steve

Jay0329-Jun-06 8:41

Jay03

29-Jun-06 8:41

A static variable is local to particular function. However, it is only initialised once (on the first call to function).

Also the value of the variable on leaving the function remains intact. On the next call to the function the the static variable has the same value as on leaving.

This is the definition I got on one of the websites
Static sounds like a CONSTANT. Replacing static with a constant sounds like the same thing.
Does that make sense to you guys????

-- modified at 14:41 Thursday 29th June, 2006

Re: Static Variables

toxcct29-Jun-06 8:58

toxcct

29-Jun-06 8:58

Jay03 wrote:
Does that make sense to you guys????

not at all !!

void inc() {
  static iCpt = 0;
  iCpt++;
  printf("%d\n", iCpt);
}
 
void main(void) {
  for (int i = 0; i < 10; i++) {
    inc();
  }
}

this code actually prints :

1
2
3
4
...

TOXCCT >>> GEII power

[VisualCalc 3.0 updated ][Flags Beginner's Guide new! ]

Re: Static Variables

Jun Du29-Jun-06 8:58

Jun Du

29-Jun-06 8:58

Jay03 wrote:
Static sounds like a CONSTANT.

No. They are different. I think you misunderstood "it is only initialised once". Look at this example:

YourFunction()
{
  static int st = 0;   // only when the function is first called
  st++;                // every time when the function is called
}

You sound pretty new to C/C++. Get a book and study it more systematically.

Best,
Jun

Re: Static Variables

David Crow29-Jun-06 8:58

Printing format of numbers

29-Jun-06 8:58

Jay03 wrote:
Static sounds like a CONSTANT.

Not even close. When a variable has static duration, it is allocated when the program begins and deallocated when the program ends. A const variable specifies that the variable is not modifiable.

"The largest fire starts but with the smallest spark." - David Crow

"Judge not by the eye but by the heart." - Native American Proverb

mikobi29-Jun-06 7:41

mikobi

29-Jun-06 7:41

I am using visual c++ 6.0;

I want to print numbers with thousand separator, what format to use.

I have float variables that i want to print like these:

252,000.00
150,250.25

What to do ?

Re: Printing format of numbers

David Crow29-Jun-06 8:10