Compiling C code in Linux

Question

I'm trying to compile a C code in Linux to make floppy music on my Raspberry Pi. I'm using Scott Vincent's code to control the GPIO pins, but I can't compile it. I'm using this command in the terminal:

gcc -o floppy_music floppy_music.c

Here is the code:

# --------------------------------------
# Written by Scott Vincent
# 16 Feb 2014
# --------------------------------------

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <wiringPi.h>

// pin 11 = wiringPi Pin 0. Use this for motor direction.
const int dirPin = 0;

// pin 12 supports pwm mode but it turns out I didn't need pwm mode in the end!
// pin 12 = wiringPi Pin 1. Use this for stepper motor.
const int stepPin = 1;

// Define an octave with naturals and sharps (Zz = rest)
enum { Cn, Cs, Dn, Ds, En, Fn, Fs, Gn, Gs, An, As, Bn, Zz };

// Define another one with flats and remaining sharps
enum { Bs, Df, Dn2, Ef, En2, Es, Gf, Gn2, Af, An2, Bf, Bn2, Zz2 };

/**
 * Frequencies in hundredths of Hz, e.g. middle A = 44000
 * 4 Octaves with 12 notes per octave, i.e. C to B
 */
const int freq[4][12] = {
   { 13081,13859,14683,15556,16481,17461,18500,19600,20765,22000,23308,24694 },
   { 26163,27718,29366,31113,32963,34923,36999,39200,41530,44000,46616,49388 },
   { 52325,55437,58733,62225,65925,69846,73999,78399,83061,88000,93233,98777 },
   { 104650,110873,117466,124451,131851,139691,147998,156798,166122,176000,186466,197553 }
};

/**
 * Frequency (in Hz) is converted to Floppy Delay using the formula:
 *   314000 / frequency = floppy delay
 * so middle A = 314000 / 440 = 714
 *
 * Lowest realistic note is delay = 1550
 * Highest realistic note is delay = 210
 */
const int floppyConv = 31400000;

// Calculate all our floppy delays at the start
int floppyDelay[4][12];

// Song1 is the C major scale (note, octave, length)
const int song1_tempo = 120;
const int song1[][3] = {
   { Cn, 1, 1 },
   { Dn, 1, 1 },
   { En, 1, 1 },
   { Fn, 1, 1 },
   { Gn, 1, 1 },
   { An, 1, 1 },
   { Bn, 1, 1 },
   { Cn, 2, 1 },
   { -1, -1, -1 }
};


// Song2 is The Imperial March from Star Wars (note, octave, length)
const int song2_tempo = 104 * 8;
const int song2[][3] = {
   { Gn, 1, 8 },      // Bar 1
   { Gn, 1, 8 },
   { Gn, 1, 8 },
   { Ef, 1, 6 },
   { Bf, 1, 2 },

   { Gn, 1, 8 },
   { Ef, 1, 6 },
   { Bf, 1, 2 },
   { Gn, 1, 16 },

   { Dn, 2, 8 },
   { Dn, 2, 8 },
   { Dn, 2, 8 },
   { Ef, 2, 6 },
   { Bf, 1, 2 },

   { Gf, 1, 8 },      // Bar 4
   { Ef, 1, 6 },
   { Bf, 1, 2 },
   { Gn, 1, 16 },

   { Gn, 2, 8 },
   { Gn, 1, 6 },
   { Gn, 1, 2 },
   { Gn, 2, 8 },
   { Gf, 2, 6 },
   { Fn, 2, 2 },

   { En, 2, 2 },
   { Ds, 2, 2 },
   { En, 2, 4 },
   { Zz, 0, 4 },
   { Gs, 1, 4 },
   { Cs, 2, 8 },
   { Bs, 2, 6 },
   { Bn, 1, 2 },

   { Bf, 1, 2 },      // Bar 7
   { An, 1, 2 },
   { Bf, 1, 4 },
   { Zz, 0, 4 },
   { Ef, 1, 4 },
   { Gf, 1, 8 },
   { Ef, 1, 6 },
   { Gf, 1, 2 },

   { Bf, 1, 8 },
   { Gn, 1, 6 },
   { Bf, 1, 2 },
   { Dn, 2, 16 },

   { Gn, 2, 8 },
   { Gn, 1, 6 },
   { Gn, 1, 2 },
   { Gn, 2, 8 },
   { Gf, 2, 6 },
   { Fn, 2, 2 },

   { En, 2, 2 },      // Bar 10
   { Ds, 2, 2 },
   { En, 2, 4 },
   { Zz, 0, 4 },
   { Gs, 1, 4 },
   { Cs, 2, 8 },
   { Bs, 2, 6 },
   { Bn, 1, 2 },

   { Bf, 1, 2 },
   { An, 1, 2 },
   { Bf, 1, 4 },
   { Zz, 0, 4 },
   { Ef, 1, 4 },
   { Gf, 1, 8 },
   { Ef, 1, 6 },
   { Bf, 1, 2 },

   { Gn, 1, 8 },
   { Ef, 1, 6 },
   { Bf, 1, 2 },
   { Gn, 1, 16 },

   { -1, -1, -1 }
};


/**
 *
 */
static void resetMotor()
{
   // To reset head position move back 10 then forward 5
   digitalWrite(dirPin, LOW);
   for (int i=0; i < 10; i++){
      digitalWrite(stepPin, HIGH);
      digitalWrite(stepPin, LOW);
      delay(1);
   }

   digitalWrite(dirPin, HIGH);
   for (int i=0; i < 5; i++){
      digitalWrite(stepPin, HIGH);
      digitalWrite(stepPin, LOW);
      delay(1);
   }

   delay(400);
}


/**
 *
 */
static int init()
{
   if (wiringPiSetup() == -1){
      printf("Failed to initialize wiringPi\n");
      return 1;
   }

   pinMode(stepPin, OUTPUT);
   pinMode(dirPin, OUTPUT);

   resetMotor();

   for (int octave = 0; octave < 4; octave++){
      for (int note = 0; note < 12; note++){
         floppyDelay[octave][note] = floppyConv / freq[octave][note];
      }
   }

   return 0;
}


/**
 *
 */
static void playNote(int note, int octave, int length)
{
   static int dir = 1;
   int pause = floppyDelay[octave][note] * 10;

   int endTime = millis() + length;
   while (millis() < endTime){
      digitalWrite(dirPin, dir);
      if (dir == 0)
         dir = 1;
      else
         dir = 0;

      digitalWrite(stepPin, HIGH);
      digitalWrite(stepPin, LOW);
      delayMicroseconds(pause);
   }
}


/**
 *
 */
static void rest(int length)
{
   int endTime = millis() + length;
   while (millis() < endTime){
      delay(5);
   }
}


/**
 * song[note_num][note, octave, length]
 */
static void playSong(const int song[][3], const int tempo)
{
   // Convert tempo in BPM to millisecs
   int noteLen = 60000 / tempo;

   for (int i = 0; song[i][0] != -1; i++){
      int length = song[i][2] * noteLen;
      if (song[i][0] == Zz){
         rest(length);
      }
      else {
         playNote(song[i][0], song[i][1], (7 * length) / 8);
         rest(length / 8);
      }
   }
}


/**
 *
 */
int main()
{
   if (init() != 0){
      printf("init failed - Exiting\n");
      return 1;
   }

   playSong(song2, song2_tempo);

   return 0;
}

And here is the error's I'm getting:

floppy_music.c:1:3: error: invalid preprocessing directive #--
floppy_music.c:2:3: error: invalid preprocessing directive #Written
floppy_music.c:3:6: error: "Feb" is not a valid filename
floppy_music.c:4:3: error: invalid preprocessing directive #--
floppy_music.c: In function 'resetMotor':
floppy_music.c:159:4: error: 'for' loop initial declarations are only allowed in C99 mode
floppy_music.c:159:4: note: use option -std=99 or -std=gnu99 to compile your code
floppy_music.c:166:13: error: redefinition of 'i'
floppy_music.c:159:13: note: previous definition of 'i' was here
floppy_music.c:166:4: error: 'for' loop initial declarations are only allowed in C99 mode
floppy_music.c: In function 'init:
floppy_music.c:191:4: error: 'for' loop initial declarations are only allowed in C99 mode
floppy_music.c:192:7: error: 'for' loop initial declarations are only allowed in C99 mode
floppy_music.c: In function 'playSong':
floppy_music.c:244:4: error: 'for' loop initial declarations are only allowed in C99 mode

But the interesting this is, that code worked for him, so does anyone know what's the problem?

You do know that comments in C don't start with `#`? For the rest, just *read* the error messages, all of them are very straight forward, and some also suggest what you should do to solve them. — Some programmer dude, Jul 12 '14 at 17:10

Jason C · Accepted Answer · 2014-07-12T17:18:43.260

6

It worked for your friend because his compiler's default settings happened to ignore invalid preprocessor directives without failing, and also accept all of that other code (which is valid in C99).

As far as the preprocessing stuff goes:

# --------------------------------------
# Written by Scott Vincent
# 16 Feb 2014
# --------------------------------------

But these aren't comments. This should be (or whatever your favorite /* ... */ style is):

/* 
  --------------------------------------
  Written by Scott Vincent
  16 Feb 2014
  --------------------------------------
*/

Or with C++-style comments (also valid with C99):

// --------------------------------------
// Written by Scott Vincent
// 16 Feb 2014
// --------------------------------------

Lines that start with # are preprocessor directives; special commands for the preprocessor that processes the file prior to compilation (e.g. #if). There is only a certain set of valid commands. These are not comments.

You could add compiler flags to make gcc accept this but it would be better to use proper comment syntax for comments and leave the # for actual preprocessing directives.

For the rest of your issues, you can do as the compiler recommends and "use option -std=99 or -std=gnu99 to compile your code". E.g. declaring variables in for loops (for (int n ...) requires at least C99.

edited Jul 12 '14 at 17:18

answered Jul 12 '14 at 17:12

Jason C

38,729
14
126
182

I got rid of the comment problems, but how should I add the options to the command? Should I keep the -o or replace it? – danrodi Jul 12 '14 at 17:19
@danrodi If you check out the [command line usage for `gcc`](http://linux.die.net/man/1/gcc) you will see that `-o` specifies the output file name. You would not want to replace that. You may want to do a little experimenting in a Linux shell and become more familiar with the concepts of command line parameters in general; it will help you out in many ways, not just with this issue, and is worth your time. – Jason C Jul 12 '14 at 17:21
Okay, but now it's giving me a bunch of undefined reference errors. – danrodi Jul 12 '14 at 17:22
@danrodi Those are separate problems. I suggest also spending a little bit of time learning how the C compiler and linker work. Have a read of http://stackoverflow.com/questions/6264249/how-does-the-compilation-linking-process-work and http://stackoverflow.com/questions/3572043/what-does-this-ld-error-undefined-reference-mean and go from there. Please do not edit your original question to include your new "undefined reference" errors. Try to solve the issues on your own first and then if you have tried something and are having problems, please ask a new, separate question. – Jason C Jul 12 '14 at 17:24

Compiling C code in Linux

1 Answers1