CODEWITHSUNDEEP
cstring
Lyrk
Lyrk

Reputation: 2000

Why can't I change char array later?

char myArray[6]="Hello"; //declaring and initializing char array

printf("\n%s", myArray); //prints Hello
myArray="World";  //Compiler says"Error expression must a modifiable lvalue

Why can't I change myArray later? I did not declare it as const modifier.

Upvotes: 5

Views: 5286

Answers (7)

Juraj Blaho
Juraj Blaho

Reputation: 13461

You cannot assign naked arrays in C. However you can assign pointers:

char const *myPtr = "Hello";
myPtr = "World";

Or you can assign to the elements of an array:

char myArray[6] = "Hello";
myArray[0] = 'W';
strcpy(myArray, "World");

Upvotes: 2

GeekFactory
GeekFactory

Reputation: 399

Well myArray is the name of the array which you cannot modify. It is illegal to assign a value to it. Arrays in C are non-modifiable lvalues. There are no operations in C that can modify the array itself (only individual elements can be modifiable).

Well myArray is of size 6 and hence care must be taken during strcpy. strcpy(myArray,"World") as it would result in overflow if the source's string length is more than the destination's (6 in this case).

A arrays in C are non-modifiable lvalues. There are no operations in C that can modify the array itself (only individual elements can be modifiable). A possible and safe method would be

char *ptr = "Hello";

If you want to change 

 ptr = strdup("World");

NOTE:

Make sure that you free(ptr) at the end otherwise it would result in memory leak.

Upvotes: 2

Bathsheba
Bathsheba

Reputation: 234715

When you write char myArray[6]="Hello"; you are allocating 6 chars on the stack (including a null-terminator).

Yes you can change individual elements; e.g. myArray[4] = '\0' will transform your string to "Hell" (as far as the C library string functions are concerned), but you can't redefine the array itself as that would ruin the stack.

Note that [const] char* myArray = "Hello"; is an entirely different beast: that is read-only memory and any changes to that string is undefined behaviour.

Upvotes: 6

amulous
amulous

Reputation: 732

You can't assign strings to variables in C except in initializations. Use the strcpy() function to change values of string variables in C.

Upvotes: 2

Yu Hao
Yu Hao

Reputation: 122403

Because the name of an array cannot be modified, just use strcpy:

strcpy(myArray, "World");

Upvotes: 3

Alok Save
Alok Save

Reputation: 206546

Array is a non modifiable lvalue. So you cannot modify it.
If you wish to modify the contents of the array, use strcpy.

Upvotes: 4

Some programmer dude
Some programmer dude

Reputation: 409216

You can't assign to an array (except when initializing it in its declaration. Instead you have to copy to it. This you do using strcpy.

But be careful so you don't copy more than five characters to the array, as that's the longest string it can contain. And using strncpy in this case may be dangerous, as it may not add the terminating '\0' character if the source string is to long.

Upvotes: 2

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