Using strncpy to remove part of a char* - c

Question

I am trying to remove a certain part of my string using strncpy but I am facing some issues here.
This is what my 2 char* has.
trimmed has for example "127.0.0.1/8|rubbish|rubbish2|" which is a
prefix of a address.
backportion contains "|rubbish|rubbish2|"
What I wanna do is to remove the backportion of the code from trimmed. So far I got this:
char* extractPrefix(char buf[1024]){
int count = 0;
const char *divider = "|";
char *c = buf;
char *trimmed;
char *backportionl;
while(*c){
if(strchr(divider,*c)){
count++;
if(count == 5){
++c;
trimmed = c;
//printf("Statement: %s\n",trimmed);
}
if(count == 6){
backportionl = c;
}
}
c++;
}
strncpy(trimmed,backportionl,sizeof(backportionl));
printf("Statement 2: %s\n", trimmed);
Which nets me an error of backportionl being a char* instead of a char.
Is there anyway I can fix this issue or find a better way to trim this char* to get my aim?

Answer 1

Here's one way that works for a list of dividers, similar to how strtok works the first time it's called:
char *extractPrefix(char *buf, const char *dividers)
{
size_t div_idx = strcspn(buf, dividers);
if (buf[div_idx] != 0)
buf[div_idx] = 0;
return buf;
}
If you don't want the original buffer modified, you can use strndup, assuming your platform supports the function (Windows doesn't; you'd need to code it yourself). Don't forget to free the pointer that is returned when you're done with it:
char *extractPrefix(const char *buf, const char *dividers)
{
size_t div_idx = strcspn(buf, dividers);
return strndup(buf, div_idx);
}
Alternatively, you could just return the number of characters (or some value less than 0 if the number of characters in the prefix won't fit in an int):
int pfxlen(const char *buf, const char *dividers)
{
size_t div_idx = strcspn(buf, dividers);
if (div_idx > (size_t)INT_MAX)
return -1;
return (int)div_idx;
}
and use it like this:
int n;
const char *example = "127.0.0.1/8|rubbish|rubbish2|";
n = pfxlen(example, "|");
if (n >= 0)
printf("Prefix: %.*s\n", n, example);
else
fprintf(stderr, "prefix too long\n");
Obviously you have a number of options. It's really up to you which one you want to use.

Answer 2

Welp, this is stupid but i fixed my issue in basically one line. so here goes,
trimmed[strchr(trimmed,'|')-trimmed] = '\0';
printf("Statement 2: %s\n", trimmed);
So by getting the index of 'backportion' from the trimmed char* using strchr, i was effectively able to fix the issue.
Thanks internet, for not much.

Answer 3

Disclaimer: I'm not sure whether I correctly understood what you actually want to achieve. Some examples would probably be helpful.
I am trying to remove a certain part of my string [..]
I have no idea what you're trying in your code, but this is pretty easy to achieve with strstr, strlen and memmove:
First, find the position of the string you want to remove using strstr. Then copy what's behind that found string to the position where the found string starts.
char cut_out_first(char * input, char const * unwanted) {
assert(input); assert(unwanted);
char * start = strstr(input, unwanted);
if (start == NULL) {
return 0;
}
char * rest = start + strlen(unwanted);
memmove(start, rest, strlen(rest) + 1);
return 1;
}