Why declare a struct that only contains an array in C?

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the expression num[1] designates the first element in the array
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I came across some code containing the following:

struct ABC {
    unsigned long array[MAX];
} abc;

When does it make sense to use a declaration like this?

It allows you to pass the array to a function by value, or get it returned by value from a function.

Structs can be passed by value, unlike arrays which decay to a pointer in these contexts.

Array of Structures in C, Declaring an array of structure is same as declaring an array of fundamental types. #include<stdio.h> #include<string.h> #define MAX 2 struct student { char If you want to increase/decrease the size of the array just change the value of the� The C language allows an array to be used as a structure member. This enables us to group related structure members and is also useful for declaring character strings as structure members. This section explains how we can effectively use such structures.

Another advantage is that it abstracts away the size so you don't have to use [MAX] all over your code wherever you declare such an object. This could also be achieved with

typedef char ABC[MAX];

but then you have a much bigger problem: you have to be aware that ABC is an array type (even though you can't see this when you declare variables of type ABC) or else you'll get stung by the fact that ABC will mean something different in a function argument list versus in a variable declaration/definition.

One more advantage is that the struct allows you to later add more elements if you need to, without having to rewrite lots of code.

Lesser known C features, The flexible array member must be the last element of the structure and the must be neither used in another structure definition nor as a member of an array. As we can see, *i has been replaced by the edx register, which is written only at� Structure in C Structure is commonly reffered to as user-defined data type. Structure is similar to an array but the only difference is that array is collection of similar data type onthe other hand structure is collection of different data type. A structure can contain any data type including array and another structure as well.

You can copy a struct and return a struct from a function.

You cannot do that with an array - unless it is part of a struct!

MEM33-C. Allocate and copy structures containing a flexible array , struct flex_array_struct { int num; int data[]; };. This definition means that when computing the size of such a structure, only the first member, num , is considered. The reason for this is that in C, we cannot equate two strings (i.e. character arrays). If we had written ' p1.name="Brown"; ', that would have given an error. Therefore, by writing strcpy (p1,"Brown"), we are copying the string 'Brown' to the string variable p1.name.

You can copy it like this.

struct ABC a, b;
........
a = b;

For an array you would need to use memcpy function or a loop to assign each element.

Explains Detail Concepts for Structure in C, Many structure variables can be declared for same structure and memory will be allocated Difference between C variable, C array and C structure: A normal C variable can hold only one data of one data type at a time. #include <string.h>. Array of Structures in C Declaring an array of structure is same as declaring an array of fundamental types. Since an array is a collection of elements of the same type. In an array of structures, each element of an array is of the structure type.

You can use struct to make a new type of data like string. you can define :

struct String {
    char Char[MAX];
};

or you can create a List of data that you can use it by argument of functions or return it in your methods. The struct is more flexible than an array, because it can support some operators like = and you can define some methods in it.

Hope it is useful for you :)

C Programming Course Notes, If only one function needs to know about a particular struct definition, then it Structs can contain arrays; Arrays can contain structs; Structs and Arrays can be� If a struct defines at least one named member, it is allowed to additionally declare its last member with incomplete array type. When an element of the flexible array member is accessed (in an expression that uses operator . or -> with the flexible array member's name as the right-hand-side operand), then the struct behaves as if the array member had the longest size fitting in the memory

Struct declaration - cppreference.com, If a struct defines at least one named member, it is allowed to additionally declare its last member with incomplete array type. When an element� For the structures in C programming language from C99 standard onwards, we can declare an array without a dimension and whose size is flexible in nature. Such an array inside the structure should preferably be declared as the last member of structure and its size is variable (can be changed be at runtime).

Structures and unions, A structure or union type definition contains the struct or union keyword the z/ OS XL C/C++ compiler supports it as an IBM extension C++ only . Flexible array members can be declared in any part of a structure, not just as the last member. Limitations of C Structures. In C language, Structures provide a method for packing together data of different types. A Structure is a helpful tool to handle a group of logically related data items. However, C structures have some limitations. The C structure does not allow the struct data type to be treated like built-in data types:

C Struct Declare Array, Sales_record is used just made from the society an answer to c struct declare an election and Mandatory to the array contains all the name, for your data? Arrays allow to define type of variables that can hold several data items of the same kind. Similarly structure is another user defined data type available in C that allows to combine data items of different kinds. Structures are used to represent a record.

Comments
  • Beware of doing this with arrays, more than say 16 or 32 bytes, for functions that don't inline: it's more efficient to pass them by const-reference, unless the callee already needs a tmp copy it can destroy. If the call / return don't optimize away, a medium to large array (thousands of bytes) is a terrible thing to pass by value.
  • (so it allows cleaner code - it won't make any difference in speed etc)
  • That's useful. Unfortunately you can't do if (a == b)!?! how inconsistent that is. For C++ it looks for an == operator. In C it says "invalid operands to binary ==".
  • Basically, it's the closest thing C has to creating a class. I like this answer because it comes the closest to pointing that out.
  • No such thing as a method in C. structs in C are plain old data. It has an = operator supported by default (which the other answers show is the reason to do this), but this is misleading and mostly applies to C++, not C.
  • @J Sternberg: "Method" is just a way of thinking about subroutines as being related to the data "objects" that they affect. You can certainly create "classes" of "objects" and "methods" that operate on them in C. The language just doesn't formally define such things. If you want to create better abstractions in C, stuffing things into a struct is usually the best way to do it.
  • In addition, if you really wanted to "create" methods in C, you could use function pointers (yes, yes, tricky syntax, no data protection, etc) to associate functions with the data that they operate on. You have to pass in "self" in the first argument (you could even name it "this", if you wanted), since there's no automatic creation of this pointer inside the function in C. Of course, it's all gymnastics, you get things like this by default in C++, though it's true there could be hidden overhead as a bonus...
  • This does not answer the question why one might use a struct containing only an array.