Function is executing when I try to store it in an array

Question

I am trying to store a set of functions with different parameter in an array. When the code enters the function songlearn with tune==1 I want the functions with set parameters to be stored in the array without executing. What am I doing wrong? Here's my code:

const int x=100;
int (*SongSeq[x])();
int note[x];
int playNote(int midi, int row, int col, int len, bool short_led = false);
void songlearn(int tune);
int tune;
void songlearn (int tune){
 if (tune==1){ 
 state=1;
 lcd.clear();
 lcd.setCursor(4,0); 
 lcd.print("Learning Song :");// Print a message to the LCD.
 lcd.setCursor(1, 1);
 lcd.print(menuP1);
// if (songpage==1){
// if (BackState==HIGH){//leaving song
// posP=0;
// Page=2; 
// Play(posP);
// }
// }
 //Plays Mary Had a Little Lamb on a loop at 145 BPM
//Bar 1
SongSeq[0]= playNote(0x40, 3, 1, 414); //Quarter note: E
note[0]=0x40;
SongSeq[1]=playNote(0x3e, 2, 4, 414); //Quarter note: D
note[1]=0x3e;
SongSeq[2]=playNote(0x3c, 2, 2, 414); //Quarter note: C
note[2]=0x3c;
SongSeq[3]=playNote(0x3e, 2, 4, 414); //Quarter note: D
note[3]=0x3e;
//Bar 2
SongSeq[4]=playNote(0x40, 3, 1, 414,1); //Quarter note: E
note[4]=0x40;
SongSeq[5]=playNote(0x40, 3, 1, 414,1); //Quarter note: E
note[5]=0x40;
SongSeq[6]=playNote(0x40, 3, 1, 828,1); //Half note: E
note[6]=0x40;
//Bar 3
SongSeq[7]=playNote(0x3e, 2, 4, 414,1); //Quarter note: D
note[7]=0x3e;
SongSeq[8]=playNote(0x3e, 2, 4, 414,1); //Quarter note: D 
note[8]=0x3e;
SongSeq[9]=playNote(0x3e, 2, 4, 828,1); //Half note: D
note[9]=0x3e;
//Bar 4
SongSeq[10]=playNote(0x40, 3, 1, 414); //Quarter note: E
note[10]=0x40;
SongSeq[11]=playNote(0x43, 3, 4, 414,1); //Quarter note: G
note[11]=0x43;
SongSeq[12]=playNote(0x43, 3, 4, 828,1); //Half note: G
note[12]=0x43;
//Bar 5
SongSeq[13]=playNote(0x40, 3, 1, 414); //Quarter note: E
note[13]=0x40;
SongSeq[14]=playNote(0x3e, 2, 4, 414); //Quarter note: D
note[14]=0x3e;
SongSeq[15]=playNote(0x3c, 2, 2, 414); //Quarter note: C
note[15]=0x3c;
SongSeq[16]=playNote(0x3e, 2, 4, 414); //Quarter note: D
note[16]=0x3e;
//Bar 6
SongSeq[17]=playNote(0x40, 3, 1, 414,1); //Quarter note: E
note[17]=0x40;
SongSeq[18]=playNote(0x40, 3, 1, 414,1); //Quarter note: E
note[18]=0x40;
SongSeq[19]=playNote(0x40, 3, 1, 414,1); //Quarter note: E
note[19]=0x40;
SongSeq[20]=playNote(0x40, 3, 1, 414,1); //Quarter note: E
note[20]=0x40;
//Bar 7
SongSeq[21]=playNote(0x3e, 2, 4, 414,1); //Quarter note: D
note[21]=0x3e;
SongSeq[22]=playNote(0x3e, 2, 4, 414,1); //Quarter note: D
note[22]=0x3e;
SongSeq[23]=playNote(0x40, 3, 1, 414); //Quarter note: E
note[23]=0x40;
SongSeq[24]=playNote(0x3e, 2, 4, 414); //Quarter note: D
note[24]=0x3e;
//Bar 8
SongSeq[25]=playNote(0x3c, 2, 2, 1656); //Whole note: C
note[25]=0x3c;
//End song
 }
 }
 int playNote(int midi, int row, int col, int len, bool short_led = false)
{
 int len1, len2;
 if (short_led) {
 len1 = len * 3 / 4;
 len2 = len * 1 / 4;
 } else {
 len1 = len;
 len2 = 0;
 }
 noteOn(0x90, midi, 100);
 digitalWrite(LedR[row], HIGH);
 digitalWrite(LedC[col], LOW);
 delay(len1);
 digitalWrite(LedR[row], LOW);
 digitalWrite(LedC[col], HIGH);
 delay(len2);
 noteOff(0x90, midi, 0);
}

• dannyf: You probably want to explain in greater detail what you meant by "storing functions in an array". It may be well understood to you but certainly not to others.

Answer 1

What you have done will certainly call the function. Since it is always the same function, just store the arguments into an array. Something like this:

const int COUNT = 100;
struct 
 {
 int midi;
 int row;
 int col; int len;
 bool short_led;
 } notes [COUNT] = {
 { 0x40, 3, 1, 414 }, //Quarter note: E
 { 0x3e, 2, 4, 414 }, //Quarter note: D
 { 0x3c, 2, 2, 414 }, //Quarter note: C
 // and so on
 };
int playNote(int midi, int row, int col, int len, bool short_led = false);
void setup() 
 {
 // put your setup code here, to run once:
 }
void loop() 
 {
 for (int i = 0; i < COUNT; i++)
 {
 if (notes [i].midi)
 playNote (notes [i].midi, notes [i].row, notes [i].col, 
 notes [i].len, notes [i].short_led);
 }
 }
int playNote(int midi, int row, int col, int len, bool short_led)
{
 int len1, len2;
 if (short_led) {
 len1 = len * 3 / 4;
 len2 = len * 1 / 4;
 } else {
 len1 = len;
 len2 = 0;
 }
 noteOn(0x90, midi, 100);
 digitalWrite(LedR[row], HIGH);
 digitalWrite(LedC[col], LOW);
 delay(len1);
 digitalWrite(LedR[row], LOW);
 digitalWrite(LedC[col], HIGH);
 delay(len2);
 noteOff(0x90, midi, 0);
}

---

yeah but i want to be able to store the function in an array with the set parameters

Do you? I wonder why.

Anyway, you can do that by making an array of lambda functions like this:

const int COUNT = 100;
int playNote(int midi, int row, int col, int len, bool short_led = false);
void (*SongSeq[COUNT])() = 
 {
 [] { playNote(0x40, 3, 1, 414); } ,
 [] { playNote(0x3e, 2, 4, 414); } ,
 [] { playNote(0x3c, 2, 2, 414); } ,
 [] { playNote(0x3e, 2, 4, 414); } ,
 // ... and so on 
 };
void setup() 
 {
 Serial.begin (115200);
 }
void loop() 
 {
 for (int i = 0; i < COUNT; i++)
 {
 if (SongSeq [i])
 SongSeq [i] ();
 }
 }
int playNote(int midi, int row, int col, int len, bool short_led)
{
 Serial.print ("Playing note ");
 Serial.println (midi);
 delay (100);
}

• Hjhk90: yeah but i want to be able to store the function in an array with the set parameters
• Hjhk90: i am getting an error: exit status 1 conflicting declaration 'void (* SongSeq [100])()'
• Nick Gammon: The second sketch I posted above compiles without errors for me under IDE 1.6.9. Have you tried that exact code?
• Hjhk90: i was able to get it to work i had an extra int (*SongSeq [100] ) in the code which i got rid of. thank you for your help and guidance
• SDsolar: Leave it to you, @Gammon. Very clever use of code.

Answer 2

Calling or entering a function means executing it -- that is just how the language is defined. A 'function' is not a construct you can manage, i.e., store or otherwise mess-with (technical term!) in the ways you might do with other kinds of data. But:

You can store a function's address (i.e., a pointer to the function) and use the pointer to call the function, and you can store its parameters just as you would store any data. So, if I understand correctly what you want to do, try something like this crude outline based on my quick read of your code. It uses stored function pointers and song-numbers and shows how to call one of those functions with the associated, stored song number as a parameter:

// Ptr to a function and a song number
typedef struct {
 void (*pfunc)(int tune);
 int tuneNum;
} SONG_T;
#define COUNT 12
void songlearn(int);
void othersongfunc(int);
// void moresongfunctions(int);
// void moresongfunctions(int);
// Table of songs & functions:
SONG_T Songs[COUNT] = {
 {songlearn, 2},
 {othersongfunc, 1},
 {songlearn, 7},
 {othersongfunc, 3},
 // etc
};
void songlearn(int)
{
 ; // does whatever it does
}
void othersongfunc(int)
{
 ; // does whatever it does
}
void somefunc(uint8_t whichSong)
{
 if( whichSong < COUNT )
 (*Songs[whichSong].pfunc)(Songs[whichSong].tuneNum);
}
void setup(void)
{
 somefunc(3);
}
void loop(void)
{
 ;
}