opening an MP3 file for bit access

Hi all,

I need to open a file of extension .mp3 in C. This file needs to give me access to it 8 bits at a time so i can send then down a physical connection. (part of an external system). However im not sure how to open a file in this way. I need advice on how to do the following:-

open file.

read 8 bits into variable (i.e. two hex characters)

loop each time reading the next 8 bits.

any advice would be greatly appreciated ive been trying to open the file in binary mode 'rb' and use 'fread' but have had no success.

Thankyou all for your time

Quote:

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any advice would be greatly appreciated ive been trying to open the file in binary mode 'rb' and use 'fread' but have had no success.

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Post the code you tried. It should work if you do it properly.

Binary mode is a good idea, especially if you're using Windows. Any sequences of CR+LF will be translated into a single newline character otherwise, which is not what you want.

fread() could read "8 bits" if you read an unsigned char. Something like this.

Code:

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unsigned char c;

fread(&c, 1, 1, fp);

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You'll have to check for EOF and probably errors too, of course.

8 bits is essentially one byte so just reading one byte would do the trick.

Quote:

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Originally Posted by Elysia

8 bits is essentially one byte

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... on most systems.

> ... on most systems.
Use CHAR_BIT from limits.h if you're unsure ;)

Hi all, thanks for the replies

The code i have been trying is as a single test project below:-

Code:

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#include <stdio.h>

int main()

{

        FILE *file_ptr;
        unsigned char data;

        int i=0;

        file_ptr = fopen("C:\\Documents and Settings\\Gareth Devine\\Desktop\\alanis_morissette_clip.mp3","rb");
        if (file_ptr !=NULL)
        {
                printf("mp3 file found\n");
               
                for (i=0;!feof(file_ptr);i++)
                        {
                               
                                fread(&data, 1, 1, file_ptr);
                                printf("%s        \n", data);
                                //would have funtion here passing the 8 bits to arm assembler code, hence the necessatity for 8 btis only!
                        }

                       
                fclose(file_ptr);
               
        }
        else
                printf("file not found\n");
        return 0;
}

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whenever i run this it finds my file, and hence enters the first if statement printing the found file to screen. Then it raises an exception "Unhandled exception at 0x004040be in mp3test.exe: 0xC0000005: Access violation reading location 0x000000ff."

Any ideas. i am using Visual C 2005 express edition if that is of any concern?

Thakyou all for you time and knowledge

Data is not a string, so you can't print it using %s. And further, it's a bad idea to use feof as loop control. You could see the FAQ for more information.
I think you can print it using %c or something, for char.

update, i ahev got the code working :)

however my PC internal speaker has decided to join in the fun!!! and beeps each time it reads a value!? any ideas?

Code:

---

#include <stdio.h>



int main()

{

        FILE *file_ptr;
        unsigned char data;

        int i=0;
        int a;

        file_ptr = fopen("C:\\Documents and Settings\\Gareth Devine\\Desktop\\alanis_morissette_clip.mp3","rb");
        if (file_ptr !=NULL)
        {
                printf("settings file found\n");
               
                for (i=0;!feof(file_ptr);i++)
                        {
                                printf("%d \n",i);
                                fread(&data, 1, 1, file_ptr);
                                printf("%c        \n", data);
                                //would have funtion here passing the 8 bits to arm assembler code, hence the necessatity for 8 btis only!
                        }

                        scanf("%d",a);
                fclose(file_ptr);
               
        }
        else
                printf("file not found\n");
        return 0;



}

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Cheers all

Don't use feof as loop control.

Elysia i have jst read the article you link to and now understand why u say this. I will chance my methods. thanks :)

Any idea over the beeping though?

cheers

do not print bynary data as %c - use %02X

Yeah, the beeping is due to some special character you print using %c, so use as vart mentions, %02X instead.

thankyou all!!!! my problems are solved. well code realted ones anyhow lol.

Your help is greatly appreciated

Gaz

The special character is character 7, I believe -- you can print it intentionally with \a.

Code:

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printf("\a");

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Great fun . . . .