如何在结构内部的结构成员上获取指针

Question

My struct are like this :

typedef struct Bounds Bounds;
struct Bounds
{
    int type;
    double lb;
    double ub;
};

typedef struct HelperGlpk HelperGlpk;
struct HelperGlpk
{
    double *matrix_coefs;
    double *obj_coefs;
    Bounds *row_bounds;
    Bounds *col_bounds;
    int *column_of_coef;
    int *row_of_coef;
    int cpt_coef;
    int cpt_contrainte;
};

I initiliaze them that way (on my main) :

HelperGlpk helper_glpk;

    helper_glpk.matrix_coefs = malloc((nbr_coefs + 1) * sizeof(double));
    helper_glpk.matrix_coefs[0] = 0;

    helper_glpk.obj_coefs = malloc((nbr_colums + 1) * sizeof(double));
    helper_glpk.obj_coefs[0] = 0;

    helper_glpk.column_of_coef = malloc((nbr_colums + 1) * sizeof(int));
    helper_glpk.column_of_coef[0] = 0;

    helper_glpk.row_of_coef = malloc((nbr_rows + 1) * sizeof(int)); 
    helper_glpk.row_of_coef[0] = 0;

    helper_glpk.col_bounds = malloc((nbr_colums + 1) * sizeof(Bounds));
    helper_glpk.row_bounds = malloc((nbr_rows + 1) * sizeof(Bounds));

    helper_glpk.cpt_coef = 1;
    helper_glpk.cpt_contrainte = 1;

Then, inside the function genere_contrainte_1() that I call this way : genere_contrainte_1(i, j, &helper_glpk, baie);

I want to access to the pointer helper_glpk->col_bounds[helper_glpk->cpt_coef]->type but I got this error :

error: invalid type argument of ‘->’ (have ‘Bounds {aka struct Bounds}’)
  helper_glpk->col_bounds[helper_glpk->cpt_coef]->type = GLP_DB;

Could you tell me what am I doing wrong ?

Edit : I DO want to access the pointer to ->type, because .type doesn't "save" the value for use outside the function genere_contrainte_1()

Answer 1

The col_bounds member of the HelperGlpk structure is being used as an array. Which is to say that

helper_glpk->col_bounds[helper_glpk->cpt_coef]

is an instance of the Bounds structure, not a pointer to a Bounds structure.

Hence, the correct syntax uses the dot notation

helper_glpk->col_bounds[helper_glpk->cpt_coef].type = GLP_DB;

Answer 2

helper_glpk->col_bounds evaluates to a Bounds* .

helper_glpk->col_bounds[helper_glpk->cpt_coef] evaluates to a Bounds .

Hence, you need to use:

helper_glpk->col_bounds[helper_glpk->cpt_coef].type = GLP_DB;
                                           // ^^ Use . not ->