read string from file, dynamically allocating memory

dynastr.c

#include <stdlib.h>
#include <stdio.h>

char * read_line( FILE * f ) {
    int cap = 32,  next = 0, c;
    char * p = malloc( cap );
    while( 1 ) { 
        if ( next == cap ) {
            p = realloc( p, cap *= 2 );
        }
        c = fgetc( f ); 
        if ( c == EOF || c == '\n' ) {
            p[next++] = 0;
            break;
        }
        p[next++] = c;
    }
    if ( c == EOF && next == 1 ) {
        free( p );
        p = NULL;
    }

    return p;
}
    
int main() {
    char * s;
    while( s = read_line( stdin ) ) {
        printf( "%s\n", s );
        free( s );
    }
}