I want to change the value of character array, when I am using like this
char *str;
fun(str);
void fun(char *str) {
str = (char *) ("changed");
}
It is not doing anything and having str as null
whereas in this manner
char *str;
fun(&str);
void fun(char **str) {
*str = (char **) ("changed");
}
It is coming fine. But I have a restriction to have the function definition as void fun(char *str), how to change the value using this usecase
I want to change the value of character array
With fun(char *str), str is a pointer. To change the value of the character array, do not change the pointer str. Change the contents of the memory str points to.
void fun(char *str) {
// str = (char *) ("changed");
str[0] = 'c';
str[1] = 'h';
str[2] = 'a';
str[3] = 'n';
str[4] = 'g';
str[5] = 'e';
str[6] = 'd';
str[7] = '\0';
// or simply
strcpy(str, "changed");
}
Be sure when calling that the pointer references available space
char buffer[100] = "Before";
printf("<%s>\n", buffer);
fun(buffer);
printf("<%s>\n", buffer);
The usual use case is that you have an array that you pass to the function. Under most circumstances, an expression of array type will be converted (or "decay") to an expression of pointer type, and the value of the pointer will be the address of the first element of the array. Example:
#define SOME_SIZE 20 // Size of the longest string you intend to store; 20 is just an example
void fun( char *str )
{
strncpy( str, "changed", SOME_SIZE );
str[SOME_SIZE] = 0; // make sure string is terminated if SOME_SIZE <= strlen("changed")
}
int main( void )
{
char buf[SOME_SIZE+1] = "foo"; // +1 for 0 terminator
printf( "buf before fun - %s\n", str );
fun( buf );
printf( "buf after fun - %s\n", str );
return EXIT_SUCCESS;
}
You're not changing the value of str itself, you're changing the contents of the buffer that str points to.
"changed", I find length as 7 and size as 8 clear. Using SOME_SIZE as the maximum length of a string in buf[] not so clear. Perhasp SOME_LENGTH?
*str = (char **) ("changed");is wrong, don't cast achar *with(char **), the first snippet is also wrong, you are changing the value of a local variable. how to change the value using this usecase: Usingstrcpy:void fun(char *str) { strcpy(str, "changed); }.strmust point to allocated space (an array or viamalloc) with space enough to store "changed"