CODEWITHSUNDEEP
carraysstringpointerschar
gta0004
gta0004

Reputation: 508

Changing the value of the original string using a pointer

I am attempting to change the value of an original string by changing a pointer.

Say I have:

char **stringO = (char**) malloc (sizeof(char*));
*stringO = (char*) malloc (17);    
char stringOne[17] = "a" ;
char stringTwo[17] = "b";
char stringThree[17] = "c";
char newStr[17] = "d";
strcpy(*stringO, stringOne);
strcpy(*stringO, stringTwo);
strcpy(*stringO, stringThree);
//change stringOne to newStr using stringO??

How can I change stringOneso its the same as newStr using the pointer stringO?

edit: I guess the question was rather unclear. i want it to modify the latest string that *strcpy was copied from. So if strcpy(*stringO, stringThree); was last called, it will modify stringThree, strcpy(*stringO, stringTwo); then string Two etc.

Upvotes: 0

Views: 152

Answers (2)

Jacob Pollack
Jacob Pollack

Reputation: 3751

I want it to modify the latest string that strcpy was copied from. So if strcpy( ( *stringO ), stringThree ); was last called, it will modify stringThree, strcpy( (*stringO ), stringTwo ); then stringTwo etc.

It is not possible to do this with your approach since you are making a copy of the string by using strcpy -- not pointing to blocks of memory. To achieve your goal I would do the following:

char *stringO = NULL;

char stringOne[ 17 ] = "a";
char stringTwo[ 17 ] = "b";
char stringThree[ 17 ] = "c";
char newStr[ 17 ] = "d";

stringO = stringOne; // Points to the block of memory where stringOne is stored.
stringO = stringTwo; // Points to the block of memory where stringTwo is stored.
stringO = stringThree; // Points to the block of memory where stringThree is stored.

strcpy( stringO, newStr ); // Mutates stringOne to be the same string as newStr.

... note that I am mutating (updating) where stringO points to, not copying a string into it. This will allow you to mutate the values in the blocks of memory that stringO points as (which is consequently where the latest stringXXX is stored) -- as requested.

Upvotes: 2

jxh
jxh

Reputation: 70402

Here's one way:

char **stringO = (char**) malloc (sizeof(char*));
char stringOne[17] = "a" ;
char stringTwo[17] = "b";
char stringThree[17] = "c";
char newStr[17] = "d";

*stringO = stringOne;
strcpy(*stringO, newStr);

If I have to use stringO the way you have allocated memory for it, then:

strcpy(*stringO, newStr);
strcpy(stringOne, *stringO);

Upvotes: 1

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