Read and edit .wav file

I have a program that manipulates .wav file to be 8bit 8000hz mono. After that I need to strip the headers and do various stuff to the samples.
I'm having trouble with stripping the .wav headers, though. I thought it would just read the file in character by character then resave without the header bytes. Unfortunately the code doesn't do what I expected. I've been working on this for a while, so I'm probably just missing something stupidly simple, but some help would be great.

Given a .wav file:

Code:

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RIFF˜WAVEfmt @@data”ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÅÅÇÇÇÇÉÉÉÑÑÑÑÑÉÇÄ}{zyxwwwxyz{{||}~ÄÅÇÇÑÖÖÖÖÑÑÑÉÇÇÅÄÄÄÄÅÇÇÑÖÜÜáááààààáÜÑÉÇÅ}|{yxwwwwxz{|~ÄÅÇÉÑÑÖÖÖÖÖÜÜÜÜÖÑÇÅÄ~~~}|{zyyxwvuttsrrrrssttuvwxyz}ÅÑáâåéèëëëëëëëêèééééééçåäâàÜÖÑÇÅÄ~}|{yyxwvuutttuvxyz|}ÅÇÉÑÖÖÜÜÖÑÑÑÉÉÅÄ~|{yxwvvuuuvvwwxyz{{zzzz{{|~ÄÅÅÇÇÉÑÜáâäåçéèéééçåãäâââââääãääâàáÜÖÖÑÉÇÅÄ~|{yxwvvuuuuvvwwwxyyzz{{{{{{{||}}~~}||{{{zzyyzz{{|}}}}||{{{|}~ÄÇÉÉÉÑÑÖÖÜàäåéèêëííëêèéçåãääääããããäâàáÜÖÑÉÇÅ~|zyxwvutttssssttuvvwxxyyzyyyz|}~}}{xvsqonnoqsuwy{}ÄÇÉÑÜáááÜÜÜÜÜÖÑÑÖÜÜáàäçëìïóôöõõöóìêåàÖÇ~}~~ÄÉÜàãéèêêêêééçãàÖÅ|yvsqolheca_]ZYWVVVWWXY[^aflszÇâêïöúûü††üûûûûùõôñîêçäáÑÅ|zxwutsrrsuwz~ÇÜâçêìïñïîìëéäáÉÄ}~

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into this code:

Code:

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void kedit(char *file)
{
    int MAX_SAMPLE = 1000000;
    int slen;
    int i;
    char sample[MAX_SAMPLE];
    char nsample[MAX_SAMPLE];
    char tempfile[175];
    FILE *wav;
    FILE *outwav;
   
   
    snprintf(tempfile, 175, "temp%s", file);
    wav = fopen(tempfile, "r");
    outwav = fopen(file, "w");
   
   
    slen = 0;   
    while( (sample[slen] = getc(wav)) != EOF)
    {
        slen++;
        printf("sample%d: %s\n", slen, sample);
    }
   
    fclose(wav);
    for(i = 12; i < slen; i++)
    {
        nsample[i-12] = sample[i];
       
        printf("nsample: %s", nsample);
        printf(" sample: %s\n", sample);
    }
    fprintf(outwav, nsample);
   
    fclose(outwav);
   
    return;
}

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I get this output:

Code:

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sample1: R
sample2: RI
sample3: RIF
sample4: RIFF
sample5: RIFF?
sample6: RIFF?
sample7: RIFF?
sample8: RIFF?
sample9: RIFF?
sample10: RIFF?
~~~~~~all the way to: sample767
nsample: f sample: RIFF?
nsample: fm sample: RIFF?
nsample: fmt sample: RIFF?
nsample: fmt  sample: RIFF?
nsample: fmt  sample: RIFF?
nsample: fmt  sample: RIFF?
nsample: fmt  sample: RIFF?
~~~~~~Repeats to 767...

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The output should be the .wav file minus the first 12 bytes. What am I doing wrong?

You probably don't want to use fprintf() to write binary data to a file. It will stop as soon as a byte is zero - because it treats zero as end of string.

Use fwrite() instead.

You may want to consider fread() for the input as well.

The input loop:

Code:

---

  while( (sample[slen] = getc(wav)) != EOF)
    {
        slen++;
        printf("sample%d: %s\n", slen, sample);
    }

---

will indicate EOF when you read a 0xFF byte, since your sample[] is a signed char, and 0xff as a signed char is -1, which is also the value of EOF. Something like this may work:

Code:

---

  int ch;
  while( (ch = getc(wav)) != EOF)
    {
        sample[slen++]  = ch;
        printf("sample%d: %s\n", slen, sample);
    }

---

--
Mats

You'll need "rb" and "wb" for the file open modes.

> (sample[slen] = getc(wav)) != EOF
You also need to read into an int variable in order to compare with EOF, and then (only if not EOF) cast it back down to a char in the assignment.

> char sample[MAX_SAMPLE];
> char nsample[MAX_SAMPLE];
2MB on the stack?
So what happens when the file is bigger than this?
Use a fixed sized block and process as you go. There is seldom any need to store the whole file in memory at once.

Quote:

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Originally Posted by Salem

> char sample[MAX_SAMPLE];
> char nsample[MAX_SAMPLE];
2MB on the stack?
So what happens when the file is bigger than this?
Use a fixed sized block and process as you go. There is seldom any need to store the whole file in memory at once.

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Thanks for the quick replies guys.
Files shouldn't be any larger than 50kb or so, as they're being sent to a satellite(in space!). I'm leaving my work building soon and heading home where I'll start implementing your suggestions, and let you know how it works out. cprogramming.com will get recognition in many documents I hand off to the bosses ;)

-student project type thing, so it's 50% learning, 50% profit for the upper guys(not me)

Sorry for double post, but I got it working, and doing what I need it to do. Thanks for all the help guys!

Code:

---

void kedit(char *file)
{
    int slen;
    int i;
    int result;
    int NUM_SKIP = 40;
    char *sample;
    char tempfile[175];
    FILE *wav;
    FILE *outwav;
   
   
    snprintf(tempfile, 175, "temp%s", file);
    wav = fopen(tempfile, "rb");
    outwav = fopen(file, "wb");
   
    fseek(wav, 0, SEEK_END);
    slen = ftell(wav);
    rewind(wav);
   
    sample = (char*) malloc (sizeof(char)*slen);
    if(sample == NULL)
    {
        fputs("Memory error", stderr);
        exit(1);
    }
   
    result = fread(sample, 1, slen, wav);
    if(result != slen)
    {
        fputs("Read error",stderr);
        exit(2);
    }
   
    fclose(wav);
    char nsample[slen-NUM_SKIP];
    for(i = slen-1; i >NUM_SKIP; i--)
    {
        nsample[i-NUM_SKIP] = sample[i];
        //Some other stuff happens in here too, but it's irrelevant to gettting this all to work.
        printf("nsample: %c", nsample[i]);
        printf(" sample: %c\n", sample[i]);
    }

    fwrite(nsample, 1, slen-NUM_SKIP, outwav);
    fclose(outwav);
   
    return;

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