Getting different values inside vs. outside a function while using global array

Question

function splitter is designed to get a string of parameters and create a an array of parameters. If only part of parameters were given, the rest of them will get default values.

for example : input string 1,2,3,4 would fill parameters array with values {"1","2","3","4"}, but if input string is 1,2, parameters={"1","2","20","0"} while parameters[3] and parameters[2] were given its default values.

BUT

when assigning default values, inside splitter the correct values are stored in parameters but when using print_output function to show parameters values - different values are shown.

in output supplied, when input is 1,2, default values should be pasted, to parameters[2], and parameters[3] , while input is 1,2,3,4 no need to use defaults.

OUTPUT:

Running string 1,2
param_2 was set to default value:20
param_3 was set to default value:0
output:
1
2
0
0
Running string 1,2,3,4
output:
1
2
3
4

CODE:

#define PARAM_AMOUNT 4
#define COLOR 1
#define LED_DELAY 20
#define BRIGHTNESS 50
#define LED_DIRECTION 0
char *parameters[PARAM_AMOUNT] = {"0", "0", "0", "0"};
int param_def[] = {COLOR, BRIGHTNESS, LED_DELAY, LED_DIRECTION};
void setup() {
 Serial.begin(9600);
 Serial.println("Running string 1,2");
 splitter("1,2");
 print_output();
 Serial.println("Running string 1,2,3,4");
 splitter("1,2,3,4");
 print_output();
}
void splitter(char *inputstr) {
 char * pch;
 int i = 0;
 pch = strtok (inputstr, " ,.-");
 while (pch != NULL)
 {
 parameters[i] = pch;
 pch = strtok (NULL, " ,.-");
 i++;
 }
 // update default values
 for (int n = i ; n <= PARAM_AMOUNT - 1; n++) {
 sprintf(parameters[n], "%d", param_def[n]);
 Serial.print("param_");
 Serial.print(n);
 Serial.print(" was set to default value:");
 Serial.println(parameters[n]);
 delay(50);
 }
}
void print_output() {
 Serial.println("output:");
 for (int n = 0 ; n <= PARAM_AMOUNT - 1; n++) {
 Serial.println(parameters[n]);
 }
}
void loop() {
 // put your main code here, to run repeatedly:
}

• Juraj: not an error, but strange n <= PARAM_AMOUNT - 1. write n < PARAM_AMOUNT
• Jot: Create a 2-dimensional array that has enough bytes or use an array with pointers so you can set the pointers to default strings. You have now a mix of those two and it is not well defined. At least write in comments what the maximum values are (how many decimal digits).
• guyd: @jot - you are write for not commenting, but each parameter in range [0,100]. integer only

Answer 1

It is not a good practice to reserve memory for a string with a constant string. Allocate an array of char arrays with:

char parameters[PARAM_AMOUNT][PARAM_LEN];

Now with "0" you allocate 2 bytes for each string. The '0' and a terminating 0.

Then in splitter function you write 3 bytes into one of the parameters with value "20". This writes outside of the 2 bytes of memory reserved for the string.

strcpy(parameters[i], pch); will copy the token returned by strtok into your array. pch points into inputstr and the delimiters in inputstr are replaced by 'strtok' with zeros

• guyd: Thank you. But but when parameters is not a pointer array, it can't get pch value... ( I guess I'm still newbie here :( )
• guyd: paramaters[i]=pch; was changed to sprintf(parameters[i],"%s",pch); now all is OK