Change C string value with pointer

Question

im trying to change a part of a string using another pointer. what I have

    char** string = (char**) malloc (sizeof(char*));
*string = (char*) malloc (100);
*string = "trololol";

char* stringP = *string;
stringP += 3;
stringP = "ABC";
printf("original string : %s\n\n", *string);
printf("stringP : %s\n\n", stringP);

What I get

original string : trololol;
stringP : ABC;

what I whant is troABCol in both of them :D

I know I have a pointer to a string (char**) because thats what I need in order to do this operation inside a method.

In C, you have to copy strings with strcpy() or memmove() or their various relatives. — Jonathan Leffler
– Jonathan Leffler, Commented Oct 15, 2012 at 15:13

nothrow · Accepted Answer · 2012-10-15 15:03:46Z

1

you need to do strcpy(*string, "trololol") instead of *string = "trololol";. Your solution brings memory leak, as it replaces the memory pointer allocated by malloc() with pointer to data, which contains the pre-allocated "trololol" string.

strcpy() copies the pure string pointed to, and instead of stringP = "ABC";, you can do memcpy(stringP, "ABC", 3) (strcpy appends \0 at the end, whereas memcpy copies only data it is told to copy).

answered Oct 15, 2012 at 15:03

nothrow

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Comments

David Grayson · Accepted Answer · 2012-10-15 15:05:38Z

0

Read Amit's answer. Also, when you write

stringP = "ABC";

you are just changing the pointer to point at a different string; you are not changing the string it was pointing at. You should look up memcpy and strcpy.

answered Oct 15, 2012 at 15:05

David Grayson

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