c - C 错误 : "Implicit declaration of function ' packet_destroy' is invalid in C99"

Question

我正在尝试对这个队列进行编程。

我的函数调用 packet_destroy(p) 时出现错误，该函数在第 69 行的函数 long queue_store (struct queue_t *q, struct packet_t *p) 中以及第 86 行的同一函数调用中“隐式声明”函数“packet_destroy”在 C99 中无效”

...现在我必须在 long queue_store (...) 中调用函数 struct packet_destroy 之前声明它吗？或者这个错误在我的代码中意味着什么？

代码:

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <limits.h>
#include <string.h>



struct packet_t {
    char *name;
    struct queue_t *queue;
};

struct queue_t {
    char *name;     // Name der Warteschlange
    int size;       // Groesse der Warteschlange
    int entries;    // Anzahl gueltige Eintraege in Warteschlange
    int time;       // Zeitstempel (werden wir erst in P6 beoetigen)
    struct packet_t **packets; // Array von Zeigern auf Pakete
    int read;       // Lese-Position (retrieve_packet())
    int write;      // Schreib-Position (store_packet())
    long lost;      // Anzahl aller verlorenen Pakete
};


struct queue_t *queue_create(char *name, int size) {
    int i;
    struct queue_t *q;           /* temporaerer zeiger auf Queue */

    q = malloc (sizeof(struct queue_t));        //dynamisch

    if (q == NULL) {
        printf("Memory allocation failed");
        return 0;
    }

    q -> name = name;
    q -> size = size;
    q -> entries = 0;
    q -> write   = 0;
    q -> read    = 0;
    q -> lost    = 0;

    return (q);
}


long queue_store(struct queue_t * q, struct packet_t * p) {

    int total = 0;
    p -> name = q -> name;


    if (q -> entries < q -> size) {

        q -> entries++;
        q -> write++;

        total ++;

        if (q -> write > q -> size) {
            q -> write = 0;
        }

        return total;
    }

    else {
        packet_destroy(p);
        q -> lost ++;
        return 0;
}
}


struct packet_t* queue_retrieve(struct queue_t *q) {


    struct packet_t *p;
    p = malloc (sizeof(struct packet_t));
    struct packet_t *queue = NULL;

    if (q -> entries > 0) {
    q -> read ++;
    q -> entries --;
    packet_destroy(p);

        if (q -> read > q -> size ) {
            q -> read = 0;
        }
    }

    return (p);
}

int queue_destroy(struct queue_t *q) {

    free(q);

}

struct packet_t* packet_create(char *p) {
    struct packet_t * packet;
    packet = malloc (sizeof(struct packet_t));

    packet -> name = p;

    return (packet);
}


int packet_destroy(struct packet_t *packet) {

    free(packet);
    return 0;
}






int main(void) {

    long i;

    struct queue_t *Q;                              // Zeiger auf Warteschlange
    struct packet_t *P;                             // Zeiger auf Paket

    clock_t start, ende;

    start = clock();

    for (i = 0; i < 1000000; i++) {
        P = packet_create ("tester");
    }
    ende = clock();
    printf("Pakete erzeugen:\n");
    printf("i     = %ld\n", i);
    printf("T[s]  = %g\n", (double) (ende - start) / CLOCKS_PER_SEC);
    printf("\n");


    start = clock();
    for (i = 0; i < 1000000; i++) {
        Q = queue_create ("test-queue mit 100 Plaetzen", 100);
    }
    ende = clock();

    printf("Queues erzeugen:\n");
    printf("i     =%ld\n", i);
    printf("T[s]  = %g\n", (double) (ende - start) / CLOCKS_PER_SEC);
    printf("\n");




    start = clock();

    Q = queue_create ("test, 100", 100);

    // Queue halb fuellen
    for (i = 0; i < 50; i++) {
        P = packet_create ("nix");
        queue_store (Q,P);
    }

    // viele Pakete erzeugen
    for (i = 0; i < 1000000; i++) {
        P = packet_create ("nix");
        queue_store (Q,P);
        P=queue_retrieve(Q);
        packet_destroy(P);
    }

    // Vorbefuellung entfernen
    for (i = 0; i < 50; i++) {
        P=queue_retrieve(Q);
        packet_destroy(P);
    }


    ende = clock();

    printf("Queue erzeugen, <Paket erzeugen, speichern,laden,zerstoeren>:\n");

    printf("i     =%ld\n", i);
    printf("T[s]  = %g\n", (double) (ende - start) / CLOCKS_PER_SEC);
    printf("\n");




    start = clock();

    Q = queue_create ("test-queue fuer 1000 Pakete", 1000);

    for (i = 0; i < 900; i++) {
        P = packet_create ("aha");
        queue_store (Q,P);

    }
    for (i = 0; i < 901; i++) {
        P=queue_retrieve(Q);
        if (NULL == P)
            printf ("kein Paket\n");
        else
            packet_destroy(P);

    }
    ende = clock();

    printf("Queue erzeugen, <Paket erzeugen, speichern,lasden,zerstoeren>:\n");

    printf("i     =%ld\n", i);
    printf("T[s]  = %g\n", (double) (ende - start) / CLOCKS_PER_SEC);
    printf("\n");


    start = clock();

    Q = queue_create ("test, 1000", 1000);

    for (i = 0; i < 900; i++) {
        P = packet_create ((int)i,0.0,0L,NULL);
        queue_store (Q,P);

    }
    for (i = 0; i < 450; i++) {
        P=queue_retrieve(Q);
        if (NULL == P)
            printf ("kein Paket\n");
        else
            packet_destroy(P);

    }
    ende = clock();

    printf("Queue erzeugen, <Paket erzeugen, speichern,laden,zerstoeren>:\n");

    printf("i     =%ld\n", i);
    printf ("Q->entries = %d\n", Q->entries);
    printf("T[s]  = %g\n", (double) (ende - start) / CLOCKS_PER_SEC);
    printf("\n");
}

Answer 1

该错误意味着您在定义函数 packet_destroy 之前尝试使用该函数，因此编译器不知道应如何调用该函数。

您可以通过将 packet_destroy 移动到任何使用它的函数之前，或者在使用该函数之前添加该函数的声明来解决此问题。