user3604802 user3604802 - 19 days ago 7
C Question

Why is my array returning the wrong values in C?

I'm trying to use the libsndfile library to read/write information between audio files.

I've managed to read the original file, write a copy of it with "watermark" values.

All I'm trying to do now is print any index where the value is not 0.

However, when I call my printBuffer() function, it's returning all 0s even though when on debug mode, I can see that the values in buffer are not zero/changing each iteration.

Am I calling the buffer array incorrectly?

I'm still new to C so if you have any suggestions they would be greatly appreciated.

Thank you.

Code:

#define _CRT_SECURE_NO_DEPRECATE
#include <stdio.h>
#include <stdlib.h>
#include <sndfile.h>
#include <time.h>

#define MAX_CHANNEL 2
#define BUF_SIZE 1024

int numItems(int frames, int channels);
void printInfo(int frames, int channels, int sampleRate);
void watermark(double *buffer, int count, int channels);
void watermark2(double *buffer, int count);
void readFile(int fileNumber);
void printBuffer(double *buffer, size_t count);

int main(void)
{

int chosenFile, answer;

printf("Please select the file you want to read\n");
printf("1. File1\n");
printf("2. File2\n");
printf("3. File3\n");
printf("4. File4\n");
printf("5. File5\n");
scanf("%d", &chosenFile);

processFile(chosenFile);
/*
Put boolean here to check whether to process the original file or the new one
*/
printf("Would you like to read the new file?\n");
printf("1. Yes\n");
printf("2. No\n");
scanf("%d", &answer);

if (answer == 1)
{
readFile(chosenFile);
}

}

int processFile(int fileNumber)
{
/*READING FILE*/

static double buffer[BUF_SIZE];
SF_INFO info;
SNDFILE *infile,*outfile;
int readCount, i;


/*
Put boolean here to check whether it should read the original files, or the new output files

*/
char *Files[] = { "File1.wav", "File2.wav", "File3.wav"
, "File4.wav", "DFile5.wav" };

char *Files2[] = { "File1Output.wav", "File2Output.wav", "File3Output.wav"
, "File4Output.wav", "File5Output.wav" };

char *inputFile = Files[fileNumber - 1];

if (!(infile = sf_open(inputFile, SFM_READ, &info)))
{
printf("Not able to open input file %s.\n", inputFile);
puts(sf_strerror(NULL));
return 1;
};


printf("You have opened: %s\n", Files[fileNumber - 1]);
printInfo( info.frames, info.channels, info.samplerate);
int num = numItems(info.frames, info.channels);
printf("Buffer(frames*channels): %d \n", num);


/*WRITING FILE*/
char *outputFile = Files2[fileNumber - 1];
printf("Your file has been saved in the following location: %s\n", outputFile);


if (!(outfile = sf_open(outputFile, SFM_WRITE, &info)))
{
printf("Not able to open output file %s.\n", outputFile);
puts(sf_strerror(NULL));
return 1;
};

/*
Actual buffer size is numItems, somehow can't declare buffer as buffer[numItems]
BUF_SIZE is set to 1024, which means that it reads the data in chunks of 1024 frames
it will keep writing in 1024 chuncks until all numItems have been written (numItems/BUF_SIZE)
Needs to be on a while loop otherwise it will only write the first 1024 frames of the file
*/


while ((readCount = sf_read_double(infile, buffer, BUF_SIZE)))
{

watermark(buffer, readCount, info.channels);
sf_write_double(outfile, buffer, readCount);
};


for (i = 0; i < sizeof(buffer) / sizeof *buffer; i++)
{
printBuffer(buffer, sizeof(buffer)/sizeof *buffer);
}


/*
Can only close SF_open once both reading/writing has been done
if you close infile after the read, it's not able to copy the audio
data from infile to write into outfile
*/
sf_close(infile);
sf_close(outfile);


return;
}

void readFile(int fileNumber)
{
SF_INFO info;
SNDFILE *infile;

char *Files[] = { "File1Output.wav", "File2Output.wav", "File3Output.wav"
, "File4Output.wav", "File5Output.wav" };

char *inputFile = Files[fileNumber - 1];

infile = sf_open(inputFile, SFM_READ, &info);

printf("You have opened: %s\n", Files[fileNumber - 1]);
printInfo(info.frames, info.channels, info.samplerate);

sf_close(infile);

return;


}

int numItems(int frames, int channels)
{
int numItems = frames * channels;
return numItems;
}
void printInfo(int frames, int channels, int sampleRate)
{
printf("Number of Frames = %d\n", frames);
printf("Number of Channels = %d\n", channels);
printf("Sample Rate = %d\n", sampleRate);
}

void watermark(double *buffer, int count, int channels)
{
double value[MAX_CHANNEL] = { 0.0, 0.0 };
int i, j;

if (channels > 1)
{
/*
Sets j to be the first channel and while i is less than 1024/5, i += channels
buffer[3] value is multiplied by 0, and set to 0
this mutes that particular index value or frame
this keeps going until i>=1024/5 and then the next channel is chosen where j = 2
buffer[4] value is multiplied by 0 and set to 0
this keeps going until i>=1024/5 where it calls back to the while loop in processFile
*/

for (j = 0; j < channels; j++)
{
for (i = j; i < count / 5; i += channels)
{
buffer[i] *= value[j];
}
}
}
else
{
/*
If audio file has 1 channel, buffer[i] is set to 0 for all values < 1024/5 frames
and it goes back to normal until the next 1024 frames where the first 1024/5 frames.
*/
for (i = 0; i < count / 5; i++)
{
buffer[i] *= value[0];
}
}

return;
}

void printBuffer(double *buffer, size_t count)
{
int i;

for (i = 0; i < count; i++)
{
if (i != 0)
printf("%d\n", buffer[i]);
}
}

/*
- *DONE* - Need to create function that will read the newly outputted file
- Find where the watermarks have been left on the audio
- Compare buffer[] values between original file and new outputted file
*/

Answer
while ((readCount = sf_read_double(infile, buffer, BUF_SIZE)))
{   

    watermark(buffer, readCount, info.channels);
    sf_write_double(outfile, buffer, readCount);
};

Here, you use the buffer again and again to read some data, watermark it and write it out.Only once you are done, you print the last remaining data out of the buffer:

for (i = 0; i < sizeof(buffer) / sizeof *buffer; i++)
{
    printBuffer(buffer, sizeof(buffer)/sizeof *buffer);
}

So, with

#define MAX_CHANNEL 2
#define BUF_SIZE 1024

and a wave file with 16 bit 44100 stereo, you will only see the last 5.8ms of sound data, which probably is almost silence, if you have normal audio like music or some high quality recorded voice with almost no noise.

Additionally: Depending on the last block read, you see the tail of the file, and then some part prior to the tail, like you see the last 3.2ms and then the 2.6ms prior to that, which was not overwritten in the last read call.

/edit: Ok, probably I got the numbers wrong, data type is double and so on, but the conceptual error is the same.

/edit 2: Looking at Jonathan Leffler's comment, I see there are even more errors ... - I recommend switching on ALL compiler warnings, and try to understand (and fix) them.