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**lovecodecakes** · 01:23 PM

I have never tried this but could something like this work? The following way I want to scanf a char * Is there a way around?

I would also like to know in a quickie
1.Pointer to a function in action, if anyone can explain it clearly with a very short example.
2. How pointer to a multidimensional array can be utilized,accessed?
thanks

Code:

int main()
{
    char *name;
    int len=0;
    puts("Enter a string");
    scanf("%s",&name);
    printf("\n string is %s",name);
}

O/P:

Enter a string
build

Process returned -1073741819 (0xC0000005) execution time : 4.625 s
Press any key to continue.

I searched, there was a question like this here:
http://www.daniweb.com/software-development/c/threads/329405/scan-a-string-to-char-name-inside-struct-data

but it still doesn't ans the question of whether we can scan straight from the *charname??

**dwise1_aol**

Code:

int main()
{
    char *name;
    int len=0;
    puts("Enter a string");
    scanf("%s",&name);
    printf("\n string is %s",name);
}

Two problems with that:
1. scanf("%s",&name); -- "%s" expects a char pointer, but name is already a char pointer, so you would not use that ampersand address operator, but rather just the char pointer variable, name.
What you are instead doing is that you are giving scanf the address of the pointer variable and telling it to store that string there. That would over-write name (AKA "clobber") with that string. If the string is (sizeof(char*) -1) or fewer characters long, then that is all that you would be damaging, but if it's longer then you will also be clobbering the memory that comes after name; eg, the int variable, len, if that's the side of name where it's stored, function control values such as the return value, arguments, stack frame location. Such clobbering will either corrupt other variables or cause the program to crash; since the process had returned a non-zero value, it looks like it crashed.

2. char *name; -- assuming that you had done the scanf correctly, there's still the problem that name is uninitialized and you would be attempting to use it before having initialized it. Where is name pointing? It does contain an address, a garbage value that just happens to have been left in that memory location after something else had used it and that is now being interpreted as a memory address where you can store that input string. But where? It's almost guaranteed to be pointing to a memory location that's already being used not only for something else, but also by some other process in which case your program will be terminated by the OS.

Before you can use a char pointer in a scanf, you need to initialize it to point to memory where it's safe to store that input string. Actually, the same applies to any function or code that's going to store a string to where the pointer is pointing. So you can assign the pointer to or into an existing char array, or you can malloc or calloc some memory and assign that address to the char pointer. But the char pointer must be initialized and it must be pointing to memory specifically designated for receiving that string.

**lovecodecakes**

@dwise assuming you mentioned, initialize it & I take that like array[] needs no "&" while scanf, char* variable name here to doesn't need either, but instead of initializing it to a char array, what I wanted was to have an array the size of what the user feeds not a pre-defined char array, the whole purpose would be defeated.

Do you mean char *name=malloc(sizeof(name))?? something like that? well not name, that's 1byte only.but something like a bigger datatype?

Is it possible at all to not use char array[] & just have a definite user defined I/p given string stored there through scanf()? Im guessing the moment user "enters", it's \n & not \0 while to not eat other memory usage of other programs upon OS, char *name needs a \0. Am I right?
Is there a way around?

Originally Posted by dwise1_aol

Code:

int main()
{
    char *name;
    int len=0;
    puts("Enter a string");
    scanf("%s",&name);
    printf("\n string is %s",name);
}

Two problems with that:
1. scanf("%s",&name); -- "%s" expects a char pointer, but name is already a char pointer, so you would not use that ampersand address operator, but rather just the char pointer variable, name.
What you are instead doing is that you are giving scanf the address of the pointer variable and telling it to store that string there. That would over-write name (AKA "clobber") with that string. If the string is (sizeof(char*) -1) or fewer characters long, then that is all that you would be damaging, but if it's longer then you will also be clobbering the memory that comes after name; eg, the int variable, len, if that's the side of name where it's stored, function control values such as the return value, arguments, stack frame location. Such clobbering will either corrupt other variables or cause the program to crash; since the process had returned a non-zero value, it looks like it crashed.

2. char *name; -- assuming that you had done the scanf correctly, there's still the problem that name is uninitialized and you would be attempting to use it before having initialized it. Where is name pointing? It does contain an address, a garbage value that just happens to have been left in that memory location after something else had used it and that is now being interpreted as a memory address where you can store that input string. But where? It's almost guaranteed to be pointing to a memory location that's already being used not only for something else, but also by some other process in which case your program will be terminated by the OS.

Before you can use a char pointer in a scanf, you need to initialize it to point to memory where it's safe to store that input string. Actually, the same applies to any function or code that's going to store a string to where the pointer is pointing. So you can assign the pointer to or into an existing char array, or you can malloc or calloc some memory and assign that address to the char pointer. But the char pointer must be initialized and it must be pointing to memory specifically designated for receiving that string.

**dwise1_aol**

Let's start of with some basic facts to keep in mind so that we can then apply them to the answers.

1. When you store a string (or anything else for that matter), it needs to go somewhere. There will be actual memory locations that will get filled. Those memory locations have to be allocated for that use. And the memory allocated needs to be of sufficient size. For built-in data types (eg, int, float, char), declaring a variable of that type satisfies those requirements.

For a C-style string, you can either declare a char array or malloc/calloc memory space from the heap. In either case, you must allocate enough space for the longest-possible string that it will hold plus one more char for the null-terminator.

DEFINITIONS:
static vs dynamic -- when you create a char array at compile time with an array declaration, then that is static because it's created before the program starts to run and cannot be changed until the program ends. When you malloc or calloc or realloc that char array during run-time, then that is creating it dynamically.

2. scanf needs memory addresses to know where to store the values it inputs. For variables of built-in types, you need to use the & address operator to convert the variable name (which represents the value that it contains) to the address of that variable. Since pointers and array names are already memory addresses, you do not use the & address operator on them.

Hopefully, keeping those two basic principles in mind will shorten my answers.