似乎找不到该结构

Question

I am trying to fetch values from a struct once its been updated however the problem am facing is an undeclared error as it cannot seem to see it.

sonicNav.h file

#include<stdio.h>
#include<stdlib.h>
#include"sonicThread.h"

extern void calcSonicS();

sonicThread.c file.

    int funcLock = 0;

    void calcSonicS() {
       struct results *rData = results;
       rData = malloc(sizeof(struct results));

       int newVal1 = rData->sens1;
       int newVal2 = rData->sens2;
       int newVal3 = rData->sens3;
       int newVal4 = rData->sens4;

       if(funcLock == 0){
       funcLock = threadFunc();//returns INT value of 1.

     }
      printf("value 1: %d value 2: %d value 3: %d value 4 %d\n", newVal1, newVal2, newVal3, newVal4);
}

sonicThread.h file

#pragma once
#include<stdio.h>
#include<stdlib.h>
#include<unistd.h>
#include<signal.h>
#include<string.h>
#include<errno.h>
#include<pthread.h>
#include<sys/time.h>
#include<wiringPi.h>


//GPIO PINS stored within structs, for each sonic range finder.
typedef struct sonicPins{
//pins and id.
int trig;
int echo;
int id;
}args;

typedef struct results{
//all pins
int sens1;
int sens2;
int sens3;
int sens4;

}rData;

sonicThread.c file

void* setup(void  *pinsPtr);
extern int threadFunc();

pthread_t pt[4];

int threadFunc()
{
  struct  sonicPins pinsArray[4] = { { 21, 20, 1 }, { 16, 12, 2 }, { 26, 19, 3 }, { 13, 6, 4 } };
  for(int i =0; i <4; i++){
  pthread_create(&pt[i], NULL, setup, &pinsArray[i] );
   }
return 1;
}

void* setup(void *pinsPtr)
{
   struct sonicPins *ptr = pinsPtr;
   int trig = 0, Echo = 0, id;
   trig = ptr->trig;
   Echo = ptr->echo;
   id = ptr->id;
   struct  results *storePtr;
}

The snippet above does update the struct "results", all threads does work concurrently each sensor giving out is own result.

Main.c

int main(){
//void(*foo1)(int, int, int);
//foo1 = &calcSonicS;

printf("In operation\n");
int operational = 1;

while(operational ==1)
{
//sonic range finders.
  calcSonicS();
//gyroscope and acceometer.
}
return 0;
}

Error output:

sonicNav.c: In function ‘calcSonicS’:
sonicNav.c:5:28: error: ‘results’ undeclared (first use in this function)
sonicNav.c:5:28: note: each undeclared identifier is reported only once for each function it appears in

Answer 1

struct results *rData = results;

error: 'results' undeclared (first use in this function)

The above line tries to declare and define a local variable named rData , which has type struct results * , and initialise it with the value of the variable (local or global) results . The error message is telling you that there is no such variable.

What you're probably mixing up is C++ (old, bad) style initialisation:

MyClass variable = MyClass();

Since the next thing you do with rData is assigning it ...

rData = malloc(sizeof(struct results));

... the solution to your issue is to just remove that "wrong initialisation" from the preceeding line altogether. You could also pack it into a single line:

struct results *rData = malloc(sizeof(struct results));

---

Looking at ...

typedef struct results{
  // ...
} rData;

... I'd guess that you have a serious misunderstanding of the relationship of structure (type) names, type names and variable names. The above definition gives you:

• The name results as structure (type) name, so it can be used after struct to name the defined structure type.
• The name rData as type name, referring to the same (structure) type as struct results .

When you then declare a variable struct results *rData you have additionally rData as name for a variable. This is possible, but far from good style.

If you remove the typedef , then things would change drastically: You'd then have a global variable named rData of type struct results .