C, howto read binary file into buffer

Scrag · 04-21-2004, 03:17 PM

Could somebody provide a complete example of code that shows how to read a binary file into a buffer/array in C. Im trying to use fread() but my C book doesnt give very understandable examples. Or if theres something better than fread thats cool too.

Thank You!!

deiussum · 04-21-2004, 03:35 PM

This is just off the top of my head, so I may miss something, but here goes:

Code:

FILE *f;
unsigned char buffer[MAX_FILE_SIZE];
int n;

f = fopen("filename.bin", "rb");
if (f)
{
    n = fread(buffer, MAX_FILE_SIZE, 1, f);
}
else
{
    // error opening file
}

The_Nerd · 04-21-2004, 04:09 PM

Code:

void ReadFile(char *name)
{
	FILE *file;
	char *buffer;
	unsigned long fileLen;

	//Open file
	file = fopen(name, "rb");
	if (!file)
	{
		fprintf(stderr, "Unable to open file %s", name);
		return;
	}
	
	//Get file length
	fseek(file, 0, SEEK_END);
	fileLen=ftell(file);
	fseek(file, 0, SEEK_SET);

	//Allocate memory
	buffer=(char *)malloc(fileLen+1);
	if (!buffer)
	{
		fprintf(stderr, "Memory error!");
                                fclose(file);
		return;
	}

	//Read file contents into buffer
	fread(buffer, fileLen, 1, file);
	fclose(file);

	//Do what ever with buffer

	free(buffer);
}

Scrag · 04-21-2004, 04:18 PM

Hhhhmmmmmm.....

With your code, it reads in (im guessing) first 4 bytes of data, which is what is happening with the different code blocks that i've written. The file is ok, its a .bmp file. The output when printing buffer is:

BM¶

Where when I cat the file its:

BM¶(*€ÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿÿ etc... etc....etc.........etc........

If im reading on the file right, and displaying it with correctly with printf("%s", buffer) , i should get lots of output to screen. I tried a for loop to read it in char by char, and output is still BM¶, and i kept an integer count with how many char's read, and its 4.
Heres the code u gave me (modified).....any other ideas??

THANKS!!

FILE *f;
unsigned char buffer[10000];
int n;

f = fopen("bmp.bmp", "rb");
n = fread(buffer, 10000, 1, f);
printf("%s\n", &buffer);

itsme86 · 04-21-2004, 04:26 PM

You can't just print a binary buffer as a string. The reason is because if the binary data contains 8-bits in a row of 0's it's interpreted as a string-terminating NULL. So let's say your buffer looks like this:

011101010101010010000101000000000001111111010100010101100

The string interprets the 00000000 as the end of the string.

If you want to show the entire contents of the buffer, then show each character one at a time until the counter equals the size of the file.

Code:

void dump_buffer(void *buffer, int buffer_size)
{
  int i;

  for(i = 0;i < buffer_size;++i)
     printf("%c", ((char *)buffer)[i]);
}

Scrag · 04-21-2004, 04:32 PM

COOL!!!

It works now, thanks to all of you !!!!!

aluser · 04-21-2004, 07:59 PM

You can also use fwrite to print the whole thing with one function call -- it's similar to fread. (Use stdout as the FILE*)

deiussum · 04-21-2004, 08:58 PM

Usually I find it's more useful to display binary data in a hexidecimal format. You can use something like:

Code:

for (int c=0;c<bufferSize;c++)
{
     printf("%.2X ", (int)buffer[c]);

     // put an extra space between every 4 bytes
     if (c % 4 == 3)
     {
         printf(" ");
     }

     // Display 16 bytes per line
     if (c % 16 == 15)
     {
         printf("\n");
     }
}
// Add an extra line feed for good measure
printf("\n");

Of course, you can also add extra stuff in there to make it look more like a hex editor as well, but you get the idea...

knockout_artist · 01-16-2008, 09:34 AM

Quote:

Originally Posted by The_Nerd

Code:

void ReadFile(char *name)
{
	FILE *file;
	char *buffer;
	unsigned long fileLen;

	//Open file
	file = fopen(name, "rb");
	if (!file)
	{
		fprintf(stderr, "Unable to open file %s", name);
		return;
	}
	
	//Get file length
	fseek(file, 0, SEEK_END);
	fileLen=ftell(file);
	fseek(file, 0, SEEK_SET);

	//Allocate memory
	buffer=(char *)malloc(fileLen+1);
	if (!buffer)
	{
		fprintf(stderr, "Memory error!");
                                fclose(file);
		return;
	}

	//Read file contents into buffer
	fread(buffer, fileLen, 1, file);
	fclose(file);

	//Do what ever with buffer

	free(buffer);
}

Good Day,
How do I read the buffer??
I have tried looping through it But I didn't any out put.

Thanks.

kishorworld · 09-23-2009, 12:38 AM

Hi friends....

m having a weather report file with extension as .wlk
it's a formatted binary data file...

Can anyone tell me that how to read this .wlk file and convert the data into the text format (.txt)with the help of C/C++ code ...

if possible provide me source code or usefule links to create programme

Email ID: kishor.j@ncmsl.com

thanx in advance...

smeezekitty · 09-23-2009, 12:51 AM

Quote:

Originally Posted by kishorworld

Hi friends....

m having a weather report file with extension as .wlk
it's a formatted binary data file...

Can anyone tell me that how to read this .wlk file and convert the data into the text format (.txt)with the help of C/C++ code ...

if possible provide me source code or usefule links to create programme

Email ID: kishor.j@ncmsl.com

thanx in advance...

your problem is more complicated
please start your own thread

theNbomr · 09-23-2009, 10:13 AM

Use the code posted by deiussum in article #8 of this thread. That won't interpret the file in any way, but simply display the bytes as hexadecimal. Interpretation of the data is application specific, and most people here won't know how to extract meaningful information from files of that type. For that, you will need some kind of published documentation, or a code library/API written for the purpose of interpreting the file.
--- rod.

smeezekitty · 09-23-2009, 12:44 PM

did you see how many views on this thread?! LOL

naphstor · 01-14-2010, 06:40 AM

hi all, i am a newbie in this forum. luckily i got the post i was searching for. but i have some issues. i have a .m4v file and want to read it and display its contents. i read the file and tried to print the buffer, but got some junk data on screen. i even tried the code given above for printing buffer, but effort seems to be in vain. The above modified code i used is :-

Code:

#include <stdio.h>

main()
{
	FILE *file;
	char *buffer;
	unsigned long fileLen;

	file = fopen("1.m4v", "rb");
	if (!file)
	{
		fprintf(stderr, "can't open file %s", "1.m4v");
		exit(1);
	}

	fseek(file, 0, SEEK_END);
	fileLen=ftell(file);
	fseek(file, 0, SEEK_SET);

	buffer=(char *)malloc(fileLen+1);

	if (!buffer)
	{
		fprintf(stderr, "Memory error!");
        fclose(file);
		exit(1);
	}

	fread(buffer, fileLen, 1, file);
	fclose(file);

	printf ("value is %s \n", &buffer);
	dump_buffer(&buffer, fileLen);
	//free(buffer);
}

dump_buffer(void *buffer, int buffer_size)
{
  int i;

  for(i = 0;i < buffer_size;++i)
     printf("%c", ((char *)buffer)[i]);
}

please help me out. thanks.

Sergei Steshenko · 01-14-2010, 08:24 AM

Quote:

Originally Posted by naphstor

hi all, i am a newbie in this forum. luckily i got the post i was searching for. but i have some issues. i have a .m4v file and want to read it and display its contents. i read the file and tried to print the buffer, but got some junk data on screen. i even tried the code given above for printing buffer, but effort seems to be in vain. The above modified code i used is :-

Code:

#include <stdio.h>

main()
{
	FILE *file;
	char *buffer;
	unsigned long fileLen;

	file = fopen("1.m4v", "rb");
	if (!file)
	{
		fprintf(stderr, "can't open file %s", "1.m4v");
		exit(1);
	}

	fseek(file, 0, SEEK_END);
	fileLen=ftell(file);
	fseek(file, 0, SEEK_SET);

	buffer=(char *)malloc(fileLen+1);

	if (!buffer)
	{
		fprintf(stderr, "Memory error!");
        fclose(file);
		exit(1);
	}

	fread(buffer, fileLen, 1, file);
	fclose(file);

	printf ("value is %s \n", &buffer);
	dump_buffer(&buffer, fileLen);
	//free(buffer);
}

dump_buffer(void *buffer, int buffer_size)
{
  int i;

  for(i = 0;i < buffer_size;++i)
     printf("%c", ((char *)buffer)[i]);
}

please help me out. thanks.

What kind of data do you expect on the screen and why do you expect it to look not like junk ? I.e. do you know what data is displayed on screen as something meaningful and what data as junk/gibberish ? If I may, have you ever heard of ASCII ? If not, try to perform web search on ASCII and/or try

man ascii

on your UNIX/Linux bix.