我如何解释这个声明？

Question

I have learned till now that the following statement:

char *ch 

declares a pointer and if we want to connect this pointer to any address we have to write it as :

char *c = &n , However I am not able to understand the meaning of following program,

#include <stdio.h>

int main()
{
    char *ch = "Hello World" ;

    printf("%s", ch) ;

    return  0 ;

}

Kindly explain me the logic behind the assign part of line 2 and why the Hello world is being printed.

Shouldn't it be *ch in place of ch in the printf?

Answer 1

According to the C Standard (6.3.2.1 Lvalues, arrays, and function designators)

3 Except when it is the operand of the sizeof operator or the unary & operator, or is a string literal used to initialize an array, an expression that has type ''array of type'' is converted to an expression with type ''pointer to type'' that points to the initial element of the array object and is not an lvalue. If the array object has register storage class, the behavior is undefined.

Thus in this declaration

char *ch = "Hello World";

in the right side there is a character literal that has type of the following array char[12] (character literals include the terminating zero '\\0')

According to the quote this array is converted to an expression that is a pointer to the first character of the array (string literal). So pointer ch is initialized by the address of the first character of the array. The literal itself stored somewhere in the static memory by the compiler.

In fact in this statement you are defining two objects: a character array (string literal) and a pointer that points to the first character of the string literal.

Though string literals in C are not constant arrays nevertheless you may not change them using such pointers. Any attempt to changes a string literal results in undefined behaviour of the program.

As for this statement

printf("%s", ch) ;

then as ch points to the first character of a string then this string is outputed according to the format specifier %s

Answer 2

"Hello World:" string will be stored into text segment of your memory and its address is assigned to *ch .

"Hello World:" is read-only,you cant modified it in later code.

Answer 3

"Hello World" is a string literal which is read-only. You can assign a pointer-to- char to a string literal as string literals gets converted to the type char* (pointer-to- char ). However, you must not write to string literals as String literals are immutable and writing to it or attempting to modify it will invoke Undefined Behavior.

^{_{Note that I'm talking about C here}}