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- gt a   12   include lt stdio h gt   include lt stdlib h gt   include lt math h gt   include  vector h   int main void       Vector  one      one- gt a   12      one- gt b   13      one- gt c   -11

User · Answer

You get the warning because you did not assign a value to one, which is a pointer. This is undefined behavior.

You should declare it like this:

Vector* one = malloc(sizeof(Vector));

or like this:

Vector one;

in which case you need to replace -> operator with . like this:

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

Finally, in C99 and later you can use designated initializers:

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

User · Answer

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- gt a   12  one- gt b   13  one- gt 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

User · Answer

When you use Vector  one you are merely creating a pointer to the structure but there is no memory allocated to it   Simply use one    Vector   malloc sizeof Vector    to declare memory and instantiate it

[c] Warning: X may be used uninitialized in this function

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