CODEWITHSUNDEEP
cstruct
carl.hiass
carl.hiass

Reputation: 1764

Suggested way to initialize a struct in C

Is there a suggested way on how to initialize a struct in C? For example:

Book romeo = {"Romeo & Juliet", "Shakespeare", 1600};

Book inferno;
inferno.title = "Divine Comedy";
inferno.author = "Dante";
inferno.year = 1400;

Is one way preferred over the other one? I would think for readability the second one is easier, but if there are a ton of fields it might become unwieldy. Additionally, is there any way to specify the variable name in the first method, something like:

Book romeo = {title="...", author="...", year="...");

Upvotes: 0

Views: 72

Answers (3)

Jaswanth
Jaswanth

Reputation: 11

Yes, there's a way but not exactly as you said.

#include <stdio.h>
typedef struct { int k; int l; int a[2]; } T;
typedef struct { int i;  T t; } S;
T x = {.l = 43, .k = 42, .a[1] = 19, .a[0] = 18 }; // x initialized to {42, 43, {18, 19} }
int main(void)
{
    S l = { 1,          // initializes l.i to 1
           .t = x,      // initializes l.t to {42, 43, {18, 19} }
           .t.l = 41,   // changes l.t to {42, 41, {18, 19} }
           .t.a[1] = 17 // changes l.t to {42, 41, {18, 17} }
          };
    printf("l.t.k is %d\n", l.t.k); // .t = x sets l.t.k to 42 explicitly
                                // .t.l = 41 would zero out l.t.k implicitly
}

Moreover, you should visit this once and please check here before you ask a question.

Upvotes: 1

chux
chux

Reputation: 153348

Is one way preferred over the other one?

Note: C defines the first as initialization, the 2nd as assignment.

Yes, global object can be initialized, but not assigned with global code.

// Possible
Book romeo = {"Romeo & Juliet", "Shakespeare", 1600};

Book inferno;

// Not possible outside a function.
inferno.title = "Divine Comedy";
inferno.author = "Dante";
inferno.year = 1400;

is there any way to specify the variable name in the first method

Since C99, members can be specified in any order, complete or not.

Book romeo = {. title = "Romeo & Juliet", .author = "Shakespeare", .year = 1600};
Book romeo = {.year = 1600, . title = "Romeo & Juliet", .author = "Shakespeare" };
Book romeo = {. title = "Romeo & Juliet", .author = "Shakespeare" };  // .year takes on value 0

Upvotes: 1

csavvy
csavvy

Reputation: 821

Additionally, is there any way to specify the variable name in the first method, something like:

hope below code helps

#include<stdio.h>

typedef struct Book {
    char *title;
    unsigned int year;
} Book;

int main() 
{
    Book B1 = { .year = 1999};
    Book B2 = {.title= "Jason Bourne",  .year = 1999};
    printf("B1.year = %d\n", B1.year);
    printf("B2.title = %s B2.year = %d\n", B2.title, B2.year);
    return 0;
}

Upvotes: 2

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