Function main received incorrect values from the subroutine - c

Question

This code does not work - issues with passing the data from subroutine to main and allocating memory.
Computations are correct inside the subroutine but the values received by the main are incorrect - variables in main has random values, eg sRates.
#include <stdio.h>
#include <malloc.h>
#include "sndfile.h"
int main(int argc, char *argv[])
{
int sRates , sRatem , ret;
long nSamples=0, nSamplem;
float *datas, *datam;
printf("Read Test\n");
if (argc != 3) {
fprintf(stderr, "Expecting two wav file as argument\n");
return 1;
}
ret = readWav(argv[1], nSamples, sRates, &datas );
if (ret != 0) {
printf("Error\n");
}
// Output Info
printf("Read %ld frames from %s, Sample rate: %d, Length: %fs\n",
nSamples, argv[1], sRates, (float)nSamples/sRates);
printf("Read %ld frames from %s, Sample rate: %d, Length: %fs\n",
nSamples, argv[1], sRates, (float)nSamples/sRates);
// free(datas);
return 0;
}
int readWav(char *fname, long *numFrames, int *sRate, float **buffer )
{
// Open sound file
SF_INFO sndInfo;
SNDFILE *sndFile = sf_open(fname, SFM_READ, &sndInfo);
if (sndFile == NULL) {
fprintf(stderr, "Error reading source file '%s': %s\n", fname, sf_strerror(sndFile));
return 1;
}
printf("1Format of the audio file = %i\n", sndInfo.format);
printf("2Number of channels = %i\n", sndInfo.channels);
printf("3Sample Rate = %d\n", sndInfo.samplerate);
printf("4 Sample count = %ld\n", (long)sndInfo.frames);
sRate= sndInfo.samplerate;
// Allocate memory
buffer = (float *)malloc(sndInfo.frames * sndInfo.channels * sizeof(float));
if (buffer == NULL) {
fprintf(stderr, "Could not allocate memory for file\n");
sf_close(sndFile);
return 1;
}
// Load data
numFrames = sf_readf_float(sndFile, buffer, sndInfo.frames);
// Check correct number of samples loaded
if (numFrames != sndInfo.frames) {
fprintf(stderr, "Did not read enough frames for source\n");
sf_close(sndFile);
free(buffer);
// return 1;
}
else {
printf("Successfully read file\n");
numFrames = sndInfo.frames;
}
// Output Info
printf("Read %ld frames from %s, Sample rate: %d, Length: %fs\n",
// numFrames, fname, sndInfo.samplerate, (float)numFrames/sndInfo.samplerate);
numFrames, fname, sRate, (float)numFrames/sndInfo.samplerate);
sf_close(sndFile);
// return(buffer);
return(0);
}

Answer 1

In C all arguments are passed by-value, so if you want a by-ref-like argument you must pass a pointer. And since you want to return a float* you need to pass a float**.
Actually you are passing that, but you are not using it correctly (please use -Wall or equivalent for your compiler to enable warnings).
The code should like more or less like this:
int readWav(const char *fname, long *numFrames, int *sRate, float **buffer)
{
*buffer = malloc(...);
//if you do not feel comfortable writing `*buffer` everywhere:
float *data = *buffer;
///....
*numFrames = sf_readf_float(...);
///....
*sRate = sndInfo.samplerate;
///....
}
int main()
{
long nSamples;
int sRates;
float *datas;
ret = readWav(argv[1], &nSamples, &sRates, &datas);
//...
}

Answer 2

You have several errors in your code
You don't declare readWav() and you call it from main(), it's working by coincidence, namely because it does return int.
You are passing the address of datas to readWav(), note that &datas has type float ** and readWav() is expecting a float *.
If you had compiler warnings turned on, youl'd have noticed this.
You are passing the value of nSamples and sRate to readWav() and you are expecting the nSamples and sRate in your main to get initialized, you need to pass their addresses instead.
You check the return value of readWav() and yet you still try to acces the datas pointer.
This is a fixed version of your code
#include <stdio.h>
#include "sndfile.h"
int readWav(const char *const fname, long *numFrames, int *sRate, float **buffer);
int main(int argc, char *argv[])
{
int sRates, sRatem, ret;
long nSamples = 0, nSamplem;
float *datas, *datam;
printf("Read Test\n");
if (argc != 3) {
fprintf(stderr, "Expecting two wav file as argument\n");
return 1;
}
ret = readWav(argv[1], &nSamples, &sRates, &datas);
if (ret != 0) {
printf("Error\n");
return 1;
}
// Output Info
printf("Read %ld frames from %s, Sample rate: %d, Length: %fs\n",
nSamples, argv[1], sRates, (float)nSamples/sRates);
printf("Read %ld frames from %s, Sample rate: %d, Length: %fs\n",
nSamples, argv[1], sRates, (float)nSamples/sRates);
free(datas);
return 0;
}
int readWav(const char *const fname, long *numFrames, int *sRate, float **buffer)
{
// Open sound file
SF_INFO sndInfo;
if ((sRate == NULL) || (numFrames == NULL) || (buffer == NULL)) {
fprintf(stderr, "Invalid arguments passed to readWav()\n");
return 1;
}
SNDFILE *sndFile = sf_open(fname, SFM_READ, &sndInfo);
if (sndFile == NULL) {
fprintf(stderr, "Error reading source file '%s': %s\n", fname, sf_strerror(sndFile));
return 1;
}
printf("1Format of the audio file = %i\n", sndInfo.format);
printf("2Number of channels = %i\n", sndInfo.channels);
printf("3Sample Rate = %d\n", sndInfo.samplerate);
printf("4 Sample count = %ld\n", (long)sndInfo.frames);
// Allocate memory
*buffer = malloc(sndInfo.frames * sndInfo.channels * sizeof(float));
if (*buffer == NULL) {
fprintf(stderr, "Could not allocate memory for file\n");
sf_close(sndFile);
return 1;
}
*sRate = sndInfo.samplerate;
// Load data
*numFrames = sf_readf_float(sndFile, *buffer, sndInfo.frames);
// Check correct number of samples loaded
if (*numFrames != sndInfo.frames) {
fprintf(stderr, "Did not read enough frames for source\n");
sf_close(sndFile);
free(*buffer);
}
else {
printf("Successfully read file\n");
*numFrames = sndInfo.frames;
}
// Output Info
printf("Read %ld frames from %s, Sample rate: %d, Length: %fs\n",
*numFrames, fname, *sRate, (float)*numFrames/sndInfo.samplerate);
sf_close(sndFile);
return(0);
}
Tip: You should try to write your function in such a way that it has only one exit point, I like using goto for that, despite what religious programmers believe about goto, it makes your code more readable consistent and maintainable.
What I mean is you can have a label where you return the error code from the function and do all the cleanup, something like this
int function()
{
/* set errorCode */
if (firstFailureCondition == 1)
goto cleanup;
if (secondFailureCondition == 1)
goto cleanup;
.
.
.
if (nthFailureCondition == 2)
goto cleanup;
cleanup:
/* do your cleanup */
return errorCode;
}