コード:

char *getline1(void)
{
    int c, capa = 1024, size = 0;
    char *data = malloc(capa);
    if (!data) return "";  // error
    while ((c = getchar()) != EOF || size != 0) {
        if (capa < size + 2) {
            char *tmp = realloc(data, capa *= 2);
            if (!tmp) return free(data), "";  // error
            data = tmp;
        }
        if (c == EOF || c == '\n') {
            data[size++] = '\n', data[size++] = '\0';
            return realloc(data, size); // return a line with just size
        }
        data[size++] = c;
    }
    free(data);
    return NULL;  // EOF
}

コード:

#include <stdio.h>
#include <stdlib.h>
 
char *getline1(void);
 
typedef struct ListItem {
    char *line;
    struct ListItem *previous;
} ListItem;
 
int main(void)
{
    ListItem *current = NULL, *next = NULL;
    char *line;
    
    while (line = getline1()) {
        if (!(next = malloc(sizeof(ListItem))))
            printf("Not enough memory.\n"), exit(1);
        if (!*line)
            printf("Error in getline1: Pointer to totally empty line!\n"), exit(1);
        next->line = line;
        next->previous = current;
        current = next;
    }
    while (current) {
        printf("%s", current->line);
        next = current->previous;
        free(current->line);
        free(current);
        current = next;
    }
 
    return 0;
}
 
struct String { char *data; int capa, size; };

int add_ch(struct String *p, int c)
{
    if (p->size >= p->capa) {
        char *tmp = realloc(p->data, p->capa *= 2);
        if (!tmp) { free(p->data); return 1; }  // error
        p->data = tmp;
    }
    p->data[p->size++] = c;
    return 0;  // no error
}

char *getline1(void)
{
    struct String s;
    s.capa = 1024, s.size = 0, s.data = malloc(s.capa);
    if (!s.data) return "";  // error

    int c;
    while ((c = getchar()) != EOF || s.size != 0) {
        if (c == EOF || c == '\n') {
            if (add_ch(&s, '\n') || add_ch(&s, '\0')) return "";  // error
            return realloc(s.data, s.size);  // return a line
        }
        if (add_ch(&s, c)) return "";  // error
    }
    free(s.data);
    return NULL;  // EOF
}

コード:

#include <stdio.h>   // getchar, fputs, stdout
#include <stdlib.h>  // malloc, free
 
char *get_ln(int n)
{
    char *p = NULL;
    int c = getchar();
    if (c != EOF || n != 0)
        if (c == EOF || c == '\n')
            (p = malloc(n+2)) && (p[n] = '\n', p[n+1] = '\0');
        else
            (p = get_ln(n+1)) && (p[n] = c);
    return p;
}

char *getline1(void) { return get_ln(0); }

int main(void)
{
    char *p = getline1();
    if (p) main(), fputs(p, stdout), free(p);
}