How to correctly use getline?

Question

I was trying to use getline for user input and I manage to do so but each time I try to print everything after %s (like .) it gets put to the next line and I am also trying to get rid of trailing space characters input so I use the function below but for some reason this isn't working, any help, sorry for anything improper still learning:

Also can I print the contents of buff like an ordinary array (for loop) or is it different if I use getline?

/******************************************************************************



*******************************************************************************/
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

int trim (char *s)
{
    int i = strlen(s) - 1;
    while (i > 0){
        if (s[i] == ' '|| s[i] == '0'){
            i--;
        }
        else {
            break;
        }
    }
    s[i + 1] = '\0';
    printf("%d\n", i);
    return (strlen(s)); 
    
}

int main()
{
    char *buff = NULL;
    size_t sizeAllocated = 0;
    printf("Begining!!\n");
    printf("> ");
    size_t numCh = getline(&buff, &sizeAllocated, stdin);
    //numCh = trim(buff);
    printf("%s.", buff);
    
    free (buff);
    buff = NULL;
    
    return 0;
}

Thank you in advance for any help

Answer 1

You have several problems:

numCh must be a ssize_t, which is the preferred type to handle errors on POSIX, use it :)

Always check the result of getline

int i = strlen(s) - 1; is very prone to errors because strlen returns an unsigned (size_t) and an empty string will give you a very big number (SIZE_MAX).

Check if this helps:

#define _POSIX_C_SOURCE 200809L

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <sys/types.h>

static char *trim(char *str)
{
    while (*str && isspace((unsigned char)*str))
    {
        str++;
    }
    if (*str)
    {
        // Here it is safe to use `strlen - 1` because
        // `if (*str)` ensures that there is a character
        char *end = str + strlen(str) - 1;

        while (*end && isspace((unsigned char)*end))
        {
            end--;
        }
        *(end + 1) = '\0';
    }
    return str;
}

int main(void)
{
    char *str = NULL;
    size_t size = 0;
    ssize_t len = 0;

    if ((len = getline(&str, &size, stdin)) != -1)
    {
        const char *trimmed = trim(str);

        printf("<%s>\n", trimmed); // Use trimmed
    }
    free(str);
    return 0;
}