Editing Lazy initialization (section)

===C===
In [[C (programming language)|C]], lazy evaluation would normally be implemented inside one function, or one source file, using [[static variable]]s.

In a function:
<syntaxhighlight lang="C">
#include <string.h>
#include <stdlib.h>
#include <stddef.h>
#include <stdio.h>

struct fruit {
    char *name;
    struct fruit *next;
    int number;
    /* Other members */
};

struct fruit *get_fruit(char *name) {
    static struct fruit *fruit_list;
    static int seq;
    struct fruit *f;
    for (f = fruit_list; f; f = f->next)
        if (0 == strcmp(name, f->name))
            return f;
    if (!(f = malloc(sizeof(struct fruit))))
        return NULL;
    if (!(f->name = strdup(name))) {
        free(f);
        return NULL;
    }
    f->number = ++seq;
    f->next = fruit_list;
    fruit_list = f;
    return f;
}

/* Example code */

int main(int argc, char *argv[]) {
    int i;
    struct fruit *f;
    if (argc < 2) {
        fprintf(stderr, "Usage: fruits fruit-name [...]\n");
        exit(1);
    }
    for (i = 1; i < argc; i++) {
        if ((f = get_fruit(argv[i]))) {
            printf("Fruit %s: number %d\n", argv[i], f->number);
        }
    }
    return 0;
}
</syntaxhighlight>
Using one source file instead allows the state to be shared between multiple functions, while still hiding it from non-related functions.

fruit.h:
<syntaxhighlight lang="C">

#ifndef _FRUIT_INCLUDED_
#define _FRUIT_INCLUDED_

struct fruit {
    char *name;
    struct fruit *next;
    int number;
    /* Other members */
};

struct fruit *get_fruit(char *name);
void print_fruit_list(FILE *file);

#endif /* _FRUIT_INCLUDED_ */
</syntaxhighlight>

fruit.c:
<syntaxhighlight lang="C">
#include <string.h>
#include <stdlib.h>
#include <stddef.h>
#include <stdio.h>
#include "fruit.h"

static struct fruit *fruit_list;
static int seq;

struct fruit *get_fruit(char *name) {
    struct fruit *f;
    for (f = fruit_list; f; f = f->next)
        if (0 == strcmp(name, f->name))
            return f;
    if (!(f = malloc(sizeof(struct fruit))))
        return NULL;
    if (!(f->name = strdup(name))) {
        free(f);
        return NULL;
    }
    f->number = ++seq;
    f->next = fruit_list;
    fruit_list = f;
    return f;
}

void print_fruit_list(FILE *file) {
    struct fruit *f;
    for (f = fruit_list; f; f = f->next)
        fprintf(file, "%4d  %s\n", f->number, f->name);
}
</syntaxhighlight>

main.c:
<syntaxhighlight lang="C">

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

int main(int argc, char *argv[]) {
    int i;
    struct fruit *f;
    if (argc < 2) {
        fprintf(stderr, "Usage: fruits fruit-name [...]\n");
        exit(1);
    }
    for (i = 1; i < argc; i++) {
        if ((f = get_fruit(argv[i]))) {
            printf("Fruit %s: number %d\n", argv[i], f->number);
        }
    }
    printf("The following fruits have been generated:\n");
    print_fruit_list(stdout);
    return 0;
}
</syntaxhighlight>