Warning: X may be used uninitialized in this function

Question

I am writing a custom "vector" struct. I do not understand why I'm getting a Warning: "one" may be used uninitialized here.

This is my vector.h file

#ifndef VECTOR_H #define VECTOR_H  typedef struct Vector{     int a;     int b;     int c; }Vector;  #endif /* VECTOR_ */ 

The warning happens here on line one->a = 12

#include<stdio.h> #include<stdlib.h> #include<math.h> #include "vector.h"  int main(void){     Vector* one;     one->a = 12;     one->b = 13;     one->c = -11; } 

Answer 1

one has not been assigned so points to an unpredictable location. You should either place it on the stack:

Vector one; one.a = 12; one.b = 13; one.c = -11 

or dynamically allocate memory for it:

Vector* one = malloc(sizeof(*one)) one->a = 12; one->b = 13; one->c = -11 free(one); 

Note the use of free in this case. In general, you'll need exactly one call to free for each call made to malloc.