I want to make a function that create a new string with a specific lenght. This is the code:
char* newString(int lenght){
char* newstring =(char*)((calloc(lenght, sizeof(char))));
newstring[lenght] = '\0';
return newstring;
}
I use it in this way:
char* string = newString(10);
My problem is that when I do:
printf("String lenght %lu \n",strlen(string));
I get 0 but I don't understand why. I am neophyte with C. Thank for your time
strlen returns the number of characters before the first '\0'. You'll get the same result if you use:
char s[10] = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
int len = strlen(s); // len will be zero.
There's a couple of issues here. The first is that you're terminating t (and I'm not sure what t references actually) with a null-terminator at index "length", which will be one greater than the size of the array. So you're accessing some random blob of memory there. The second is improperly using calloc. I think you want something more like:
char* new_string(int length) {
char* new_string;
new_string = malloc(sizeof(char) * length);
memset(new_string, 0, length);
new_string[length-1] = '\0';
return new_string;
}
Strlen in your example returns 0 because it counts the characters before the null terminator, which happens to be 0 in your implementation.
calloc is correct. You do the same exact thing, just with more lines of code. Technically, all this function has to do is return calloc(length, sizeof(char));
If length doesn't include the null termination then you should set t[length - 1] to zero, or alternatively calloc with size length + 1.
strlen(string) reports 0.strlen count the number of character in the c string until it see a "\0" (end of string) so as your string is initialized with "\0" its length is actually 0. change this value to another one like.
memcpy(string, "good things", 10);
printf("%d", strlen(string));
calloczero initializes your array, and you never populate it with anything. Also, it's spelled "length"t[lenght] = '\0'regardless, thus invoking undefined behavior. Arrays in C are zero-base-indexed. Meaning0...(lenght-1)are the allowable range of indexes..t[length] = '\0';is an out of bound write.