Say I have an array of longs, and some of the terminating elements might be NULL.

long array[30] = [172648712, 27146721, 27647212, NULL, NULL]

and I want to convert this array to an ASCII string separated by \n.

I want

char bufOut[MAXLINE] = "172648712\n27146721\n27647212"

How would I go about doing this in C? Of course in Python it would just be "\n".join(array) but life isn't that easy down this low.

CodePudding user response：

A longer, but perhaps more clear version. Explanations are in the comments

#include<stdio.h>
#include<string.h>

#define MAXLINE 512

int main(void)
{
    // correctly define array with brackets, end with 0 terminator
    long array[30] = {172648712, 27146721, 27647212, 0};
    // create a string MAXLINE long, initialized to '\0'
    char buf[MAXLINE] = { 0 };
    // initialize its string length to 0
    size_t strLen = strlen(buf);
    // loop until array contains a 0 value. If it does not contain a zero, this could
    // search beyond the array bounds invoking UB
    for (int i=0; array[i] != 0; i  )
    {
        // plenty of space for a long
        char temp[32];
        // write the array value to a temp string with a trailing newline, checking how many
        // bytes were written
        strLen  = sprintf(temp, "%ld\n", array[i]);
        // checking -1 because sprintf return does not include the NUL terminator
        if (strLen < sizeof(buf) - 1)
        {
            // append temp to buf
            strcat(buf, temp);
        }
        else
        {
            // our string is out of space, handle this error how you want. If buf
            // was dynamically allocated, here you could realloc and continue on
            fprintf(stderr, "Source string out of space");
            break;
        }
    }

    printf("%s", buf);

    return 0;
}

Demo

CodePudding user response：

char *convert(char *buff, const long *array, const long sentinel, size_t size)
{
    char *wrk = buff;
    while(size-- && *array != sentinel)
    {
        wrk  = sprintf(wrk, "%ld%s", *array, (size && array[1] != sentinel) ? "\n" : "");
        array  ;
    }
    return buff;
}