I have this code but I don't know what happen why the result of out is incorrect any advice please?

int *getarray(int *out)  
{  
    int data[20];  
    for(int i=0;i<20;i  )  
    {  
       data[i]=i;
    } 
    for(int i=0;i<20;i  )  
    {  
       out =data[i]; 
    }  
    Serial.printf("out inside getarray = %d",out);

    return data;  
}  

void resultdata(){
  int *n;  
  int out;
  n=getarray(&out); 
  Serial.printf("out = %d",out);   
} 
void setup() {
  // Init Serial Monitor
  Serial.begin(115200);
 resultdata();
}

CodePudding user response：

Two problems:

• The data array in getarray will cease to exist once the getarray function has finished execution.
• You need to dereference out in order to change the out in resultdata. Read again the chapter dealing with pointers in your learning material.

You probably want something like this:

int *getarray(int *out, int *data)  
{  
    // remove this   int data[20];  
    *out = 0;            // you need to dereference the out pointer
                         // and initialize it to 0

    for (int i = 0; i < 20; i  )  
    {  
       data[i] = i;      // you need to dereference the out pointer
       *out  = data[i]; 
    } 

    // I'm not sure why you have this second loop here,
    // it looks pretty pointless
    for (int i = 0; i < 20; i  )  
    {  
       *out  = data[i];  // you need to dereference the out pointer
    }

    Serial.printf("*out inside getarray = %d", *out);

    return data;  
}

void resultdata(){
  int *n;  
  int out;
  int data[20];              // declare the data array here
  n = getarray(&out, data);  // pass address of the data array
                             // so that getarray can fill the data array
  Serial.printf("out = %d", out);   
}