WAV File Reader / Writer C++

Audio.cpp

#pragma once

#include "Audio.h"

Audio::Audio(std::string str) {
	if (str.substr(str.size() - 4) != ".wav")
		throw std::invalid_argument("Can only read WAV files!");
	load_wav(str);
}

void Audio::load_wav(std::string str) {
	FILE *fp;
	errno_t err = fopen_s(&fp, str.c_str(), "rb");
	if (err != 0)
		throw std::runtime_error("Error opening file!");

	// Chunk
	fread(type, sizeof(char), 4, fp);
	if (strcmp(type, "RIFF"))
		throw std::runtime_error("Not a RIFF file!");

	fread(&ChunkSize, sizeof(int), 1, fp);
	fread(format, sizeof(char), 4, fp);
	if (strcmp(format, "WAVE"))
		throw std::runtime_error("Not a WAVE format!");

	// 1st Subchunk
	fread(Subchunk1ID, sizeof(char), 4, fp);
	if (strcmp(Subchunk1ID, "fmt "))
		throw std::runtime_error("Missing fmt header!");
	fread(&Subchunk1Size, sizeof(int), 1, fp);
	fread(&AudioFormat, sizeof(short), 1, fp);
	fread(&NumChannels, sizeof(short), 1, fp);
	fread(&SampleRate, sizeof(int), 1, fp);
	fread(&ByteRate, sizeof(int), 1, fp);
	fread(&BlockAlign, sizeof(short), 1, fp);
	fread(&BitsPerSample, sizeof(short), 1, fp);

	// 2nd Subchunk
	fread(Subchunk2ID, sizeof(char), 4, fp);
	if (strcmp(Subchunk2ID, "data")!=0)
		throw std::runtime_error("Missing data header!");
	fread(&Subchunk2Size, sizeof(int), 1, fp);
	// Data

	//Subchunk2Size = NumSamples * NumChannels * BitsPerSample/8
	int NumSamples = Subchunk2Size / (NumChannels*(BitsPerSample / 8));

	data = std::vector<std::pair<short, short> >(NumSamples);
	for (int i = 0; i < NumSamples; i++) {
		fread(&data[i].first, sizeof(short), 1, fp);
		fread(&data[i].second, sizeof(short), 1, fp);
	}
	fclose(fp);
}

void Audio::write_wav(std::string str) {
	FILE *fp;
	fopen_s(&fp, str.c_str(), "wb");

	fwrite(type, sizeof(char), 4, fp);
	fwrite(&ChunkSize, sizeof(int), 1, fp);
	fwrite(format, sizeof(char), 4, fp);

	// 1st Subchunk
	fwrite(Subchunk1ID, sizeof(char), 4, fp);
	fwrite(&Subchunk1Size, sizeof(int), 1, fp);
	fwrite(&AudioFormat, sizeof(short), 1, fp);
	fwrite(&NumChannels, sizeof(short), 1, fp);
	fwrite(&SampleRate, sizeof(int), 1, fp);
	fwrite(&ByteRate, sizeof(int), 1, fp);
	fwrite(&BlockAlign, sizeof(short), 1, fp);
	fwrite(&BitsPerSample, sizeof(short), 1, fp);

	// 2nd Subchunk
	fwrite(Subchunk2ID, sizeof(char), 4, fp);
	fwrite(&Subchunk2Size, sizeof(int), 1, fp);
	
	// Ideally instead of the for loop there would be something like
	// fwrite(&data[0], sizeof(short), data.size(), fp);
	// But I have pairs and they have to be written interchangebly like right,left right,left right,left...

	for (int i = 0; i < data.size(); i++) {
		fwrite(&data[i].first, sizeof(short), 1, fp);
		fwrite(&data[i].second, sizeof(short), 1, fp);
	}
	fclose(fp);
}

Audio.h

#pragma once

//#define _CRT_SECURE_NO_DEPRECATE

#include <vector>
#include <utility>
#include <string>
#include <stdexcept>
#include <iostream>
#include <stdio.h>
#include <cstring>

class Audio {
public:
	// Constructors
	Audio(std::string str);
	Audio() {};

	// Read / Write files
	void load_wav(std::string str);
	void write_wav(std::string str);

	// Get functions
	// Subchunk2Size = NumSamples * NumChannels * BitsPerSample / 8 <==> NumSamples = Subchunk2Size / (NumChannels*(BitsPerSample / 8))
	unsigned get_size() { return data.size(); }
	unsigned get_sample_rate() { return SampleRate; }
	unsigned get_n_channels() { return NumChannels; }

	// Set Functions
	void set_sample_rate(int n) { SampleRate = n; }
	void set_n_channels(int n) { if (n != 1 && n != 2)throw std::invalid_argument("n can only be 1 (MONO) or 2 (STEREO)!"); NumChannels = n; }

	// Overloaded Operators
	std::pair<short, short> &operator[](unsigned i) { return data[i]; }
protected:
	char type[5];
	char format[5];
	char Subchunk1ID[5];
	char Subchunk2ID[5];

	int ChunkSize;
	int Subchunk1Size;
	int SampleRate;
	int ByteRate;
	int Subchunk2Size;

	short AudioFormat;
	short NumChannels;
	short BlockAlign;
	short BitsPerSample;

	// utility
	unsigned NumSamples;

	std::vector<std::pair<short, short> > data;
};

In Audio.h file line 31:

void set_n_channels(int n) { if (n != 1 || n != 2)throw std::invalid_argument("n can only be 1 (MONO) or 2 (STEREO)!"); NumChannels = n; }

That logic statement (n != 1 || n != 2) is always true for any n. As a result, it always throws.
Change that to be (n != 1 && n != 2) should fix it.

Please apply the fix to this file in github.

Audio.cpp doesn't work. This problem was found when I let it read a 720KB wav file. It throws at this code:

	if (strcmp(Subchunk2ID, "data"))
		throw std::runtime_error("Missing data header!");

Debug found the read-in Subchunk2ID is "LIST", not "data" expected by the code.
I commented out above 2 lines and it could complete the 2 functions load_wav() and write_wav().
But the output audio file is only 68 bytes and got error when trying to play that audio file.
Original 720KB input audio file can be played with no problem.

Thanks for reporting those issues. I have fixed the issue with set_n_channels. However, I don't plan to expand this gist any further. It's just some example code - it's not meant to be a library. For a more stable implementation, I would suggest using an audio library for C++.

	memset(format,0,sizeof(format));
	memset(Subchunk1ID,0,sizeof(Subchunk1ID));
	memset(Subchunk2ID,0,sizeof(Subchunk2ID));