Right methods of copying strings with malloc-CodePudding

I want to copy the string “Best School” into a new space in memory, which of these statements can I use to reserve enough space for it

A. malloc(sizeof(“Best School”))

B. malloc(strlen(“Best School”))

C. malloc(11)

D. malloc(12)

E. malloc(sizeof(“Best School”) 1)

F. malloc(strlen(“Best School”) 1)

I am still very new to C programming language so I really am not too sure of which works well. But I will love for someone to show me which ones can be used and why they should be used.

Thank you.

CodePudding user response：

Literal strings in C are really arrays, including the null-terminator.

When you use sizeof on a literal string, you get the size of the array, which of course includes the null-terminator inside the array.

So one correct way for a literal string would be sizeof("Best School") (or sizeof "Best School").

You can also use strlen. If you don't have a string literal but another array or a pointer to the first character of the string, then you must use strlen. But now you have to remember that strlen returns the length of the string without the null-terminator. So you need to add one for that.

So another correct way would then be strlen("Best School") 1.

Using magic numbers is almost never correct.

CodePudding user response：

Use of sizeof id limited to only this one case (string literal). Ti will not work if you will have a pointer referencing the string. Before you start to be more proficient in C language and "feel" the difference between arrays and pointers IMO you should always use strlen

Example:

char *duplicateString(const char *str)
{
    char *newstring = malloc(strlen(str)   1);
    if(newstring) strcpy(newstring, str);
    return newstring;
}

In this case, sizeof(str) would give the size of the pointer to char (usually 2, 4 or 8) not the the length of the string referenced by the str