Result of sizeof for C++ arrays and pointers

sizeof operator in c
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On an x86_64 architecture, a pointer is 8 bytes. It makes sense to me that sizeof(x) should return 8. I understand that a char is a single byte, and 5 bytes is the size of array z. What is the intuition behind why sizeof(z) does not return 8?

int* x = new int[10];
char z[5];

// Returns 8
std::cout << "This is the size of x: " << sizeof(x) << std::endl;

// Returns 5
std::cout << "This is the size of z: " << sizeof(z) << std::endl;

What is the intuition behind why sizeof(z) does not return 8?

z is not a pointer. Hence sizeof(z) is not anything, but 5 bytes. In case of sizeof, the array doesn't decay to pointer. Refer: What is array decaying?


There are several implicit conversions in C++ like array to pointer, enum to integer, double to float, derived to base, any pointer to void* and so on. Which may lead us to think if their sizes are same or what? Hence, a litmus test for self understanding is to create a pointer reference & try to assign the other type. It results in error for non matching types. e.g.

int *x = new int[5], *&px = x; // OK
int z[5], *&pz = z; // error: can't initialize

Sizeof operator in C, The sizeof operator is the most common operator in C. It is a compile-time unary operator and used to compute the size of its operand. It returns� sizeof (char), sizeof (char8_t), sizeof (signed char), sizeof (unsigned char), and sizeof (std:: byte) are always equal to 1. sizeof cannot be used with function types, incomplete types, or bit-field glvalues. When applied to a reference type, the result is the size of the referenced type.


You've defined x as a pointer to char, so sizeof(x) yields the size of a pointer to char. On a current implementation, that'll typically be either 32 bits or 64 bits. A char is typically 8 bits, so you can expect sizeof(char *) to yield 4 or 8 on most current compilers.

You've defined z as an array of 5 char, so sizeof(z) yields the size of an array of 5 char. Since the elements of an array are contiguous, and sizeof(char) is guaranteed to be 1, the obvious value for that would be 5.

If (for example) you put an array of 5 char into a struct, and that's followed by (say) an int, there's a very good chance the compiler will insert some padding between those two elements.

sizeof operator - cppreference.com, Temporary materialization, however, is (formally) performed for prvalue arguments: sizeof determines the size of the result object. (since C++17)� The result of sizeof for an array operand is number of elements in the array multiplied by size of an element in bytes. So value of the expression TOTAL_ELEMENTS in the above program is 7. The data type of the sizeof result is unsigned int or unsigned long depending upon the compiler implementation.


Every character have size of '1' Suppose when you compile it

 //It returns 1
      char z='a';
     std::cout << "This is the size of z: " << sizeof(z) << std::endl;
//It returns 5 because it is an array of 5 characters
 char z[5];
std::cout << "This is the size of z: " << sizeof(z) << std::endl;

sizeof, The sizeof() function in C is a built-in function that is used to calculate the size (in Note: The result of the sizeof() function is machine-dependent since the sizes� sizeof gives you the size in bytes, not the number of elements. As Alok says, to get the number of elements, divide the size in bytes of the array by the size in bytes of one element. The correct C idiom is: sizeof a / sizeof a[0]


When you pass an array name to sizeof, you want to know how many "bytes" of data belong to this array.

When you pass a pointer to sizeof, you want to know how many "bytes" does this pointer occupy.

The difference is very obvious when you pass an array name as a function argument. In this case the function cannot see the whole data area the array occupies. It only see the "pointer" type.

What is the sizeof() function in C?, The sizeof operator gives the amount of storage, in bytes, required to When you apply the sizeof operator to an array identifier, the result is� When sizeof is applied to the name of an array, the result is the number of bytes required to store the entire array. This is one of the few exceptions to the rule that the name of an array is converted to a pointer to the first element of the array, and is possible just because the actual array size is fixed and known at compile time, when the sizeof operator is evaluated.


The size of a pointer depends on many factors - including the CPU architecture, compiler, Operating System etc.

So, for a 32bit computer, the pointer size can be 4 bytes while 64bit computers can have 8 bytes(Keyword: "can"). Or, a 64bit computer running a 32bit OS will have 4 bytes. Still, under a specific architecture, all types of pointers (void*, int*, char*, long* etc) will have same size (except function pointers).

That's, pointers in C (or C++) don't have a fixed size.

sizeof Operator (C), I was mucking around looking for similar functionality when I stumbled on this: Is it possible to print out the size of a C++ class at compile-time? Which gave me� The sizeof operator is the most common operator in C. It is a compile-time unary operator and used to compute the size of its operand. It returns the size of a variable.


How can I print the result of sizeof() at compile time in C?, sizeof cannot be used with function types, incomplete types, or bit-field lvalues. When applied to an operand that has structure or union type, the result is the total � C/C++ sizeof() Operator: In this tutorial, we are going to discuss the details about the sizeof() operator in C/C++ starting from its usage, examples to applications. Submitted by Radib Kar, on July 07, 2020 Definition of sizeof() operator


sizeof operator, using the sizeof operator. This page contains example on computing the size of int, float, char and double of a system using sizeof operator in C programming. The result of sizeof is of unsigned integral type which is usually denoted by size_t. sizeof can be applied to any data-type, including primitive types such as integer and floating-point types, pointer types, or compound datatypes such as Structure, union etc.


C Program to Find the Size of int, float, double and char, SizeOf operator is mostly used to find the array size, structure size, and do some calculations as per the results. The C sizeof operator returns the size (number of � The syntax of using sizeof is as follows − sizeof (data type) Where data type is the desired data type including classes, structures, unions and any other user defined data type. Try the following example to understand all the sizeof operator available in C++. Copy and paste following C++ program in test.cpp file and compile and run this program.