How to return float value from parameter-CodePudding

I need to get float value from parameter

float aCoefficiants[50]=
{
-0.000890288188976378,
..
}
float bCoefficiants[50] =
{
 
89.1324281858268,
..
}

   float* cArray ;
   Get_Coefficient_From_Value(2211,(float*)&cArray);
   printf(">> out %f %f",cArray[0],cArray[1]);

And function:

void Get_Coefficient_From_Value(int32_t pulse, float * coefficient)
{
 
     coefficient[0] = aCoefficiants[0];
     coefficient[1] = bCoefficiants[0];
    printf(">> in %f %f\n",(coefficient[0]),(coefficient[1]));

}

in parameter that I expected: >> in -0.000890 89.132431 But out values does not match with original >> out-0.001010 99.323250

How get float variables in parameter corrrectlu and solve this problem?

EDIT:

https://onlinegdb.com/Jy_ylNlVf

CodePudding user response：

float* cArray;

That is an uninitialised pointer and dereferencing it results in Undefined Behaviour. Change that to an actual array. The following complete program should work.

#include <stdio.h>
#include <stdint.h>
 
void Get_Coefficient_From_Value(int32_t pulse, float * coefficient)
{
    coefficient[0] = -0.000890288188976378;
    coefficient[1] = 89.1324281858268;
    printf(">> in %f %f\n",(coefficient[0]),(coefficient[1]));
 
}
 
int main(void)
{
   float cArray[2];
   Get_Coefficient_From_Value(2211, cArray);
   printf(">> out %f %f",cArray[0],cArray[1]);
   return 0;
}

CodePudding user response：

This is undefined behavior:

float* cArray ;
Get_Coefficient_From_Value(2211,(float*)&cArray);

cArray is not pointing to anything valid. Further, you are casting the pointer to cArray to a float pointer and passing that in. (Technically, the pointer to an array is the array, but I digress).

Hence, when that function writes into cArray[0] and cArray[1], you are stomping on memory that doesn't belong to you.

Better:

float cArray[2] = {0};
Get_Coefficient_From_Value(2211,cArray);

When you invoke it that way, the cArray array will "degrade to a pointer" when passed in as a parameter. The two coEfficient assignments in that function will moving values into valid memory.