[英]Valgrind Invalid read of size 4 with linked list in C
我在 C 語言中的鏈表遇到了一些問題。我實際上正在做一個項目,使用套接字與服務器和客戶端連接。 我決定為我的客戶使用鏈接列表。 這是我的結構:
typedef struct ClientsList_s {
int sockfd;
struct ClientsList_s *next;
} ClientsList_t;
因此,當我使用 valgrind 執行工作時,我從 6 個上下文中得到了 6 個錯誤。 這是一個錯誤的示例:
Invalid read of size 4
==33211== at 0x109531: get_max_socket (server.c:26)
==33211== by 0x1097C2: do_server_loop (server.c:80)
==33211== by 0x109A40: launch_teams (main.c:53)
==33211== by 0x109AE6: main (main.c:63)
==33211== Address 0x4a58040 is 0 bytes inside a block of size 16 free'd
==33211== at 0x483CA3F: free (in /usr/lib/x86_64-linux-
gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
==33211== by 0x109675: receive_socket_message (server.c:47)
==33211== by 0x109832: do_server_loop (server.c:86)
==33211== by 0x109A40: launch_teams (main.c:53)
==33211== by 0x109AE6: main (main.c:63)
==33211== Block was alloc'd at
==33211== at 0x483B7F3: malloc (in /usr/lib/x86_64-linux-
gnu/valgrind/vgpreload_memcheck-amd64-linux.so)
==33211== by 0x10937B: add_client (client.c:18)
==33211== by 0x109777: check_new_socket (server.c:68)
==33211== by 0x109816: do_server_loop (server.c:84)
==33211== by 0x109A40: launch_teams (main.c:53)
==33211== by 0x109AE6: main (main.c:63)
這是錯誤來自的函數:
static int get_max_socket(MasterSocket_t *server, ClientsList_t **clients)
{
int maxSd = server->sockfd;
ClientsList_t *temp = *clients;
FD_ZERO(&server->readfds);
FD_SET(server->sockfd, &server->readfds);
while (temp != NULL) {
if (temp->sockfd > 0)
FD_SET(temp->sockfd, &server->readfds);
if (temp->sockfd > maxSd)
maxSd = temp->sockfd;
temp = temp->next;
}
return (maxSd);
}
因此,當我關閉客戶端並且服務器仍在運行時,會出現所有錯誤。 我在 while 中使用 temp 的每一行都會給我一個錯誤。 所以首先我認為這是一個初始化問題,但似乎並非如此。 這是我的功能:
void add_client(ClientsList_t **clients, int newSocket, int port)
{
ClientsList_t *temp = NULL;
ClientsList_t *last = *clients;
temp = malloc(sizeof(ClientsList_t));
temp->sockfd = newSocket;
temp->next = NULL;
if (*clients == NULL)
*clients = temp;
else {
while (last->next != NULL)
last = last->next;
last->next = temp;
}
}
還有一個功能,當我關閉他的客戶時,我會破壞一個元素:
static void receive_socket_message(ClientsList_t **clients,
MasterSocket_t *server)
{
ClientsList_t *temp = *clients;
ClientsList_t *tempDel = NULL;
int valread = 0;
int addrlen = 0;
char buffer[1025];
while (temp != NULL) {
if (FD_ISSET(temp->sockfd, &server->readfds)) {
if ((valread = read(temp->sockfd, buffer, sizeof(buffer))) == 0) {
tempDel = temp;
temp = temp->next;
close(tempDel->sockfd);
free(tempDel);
continue;
} else {
buffer[valread] = '\0';
printf("%s\n", buffer);
}
}
temp = temp->next;
}
}
如果你想測試一些東西,有我的循環功能:
static int check_new_socket(ClientsList_t **clients,
MasterSocket_t *server, int port)
{
int newSocket = 0;
if (FD_ISSET(server->sockfd, &server->readfds)) {
if ((newSocket = accept(server->sockfd,
(struct sockaddr *)&server->address,
(socklen_t *)&server->addrlen)) < 0)
return (-1);
add_client(clients, newSocket, port);
}
return (0);
}
int do_server_loop(MasterSocket_t server, int port)
{
int maxSd = 0;
int activity = 0;
ClientsList_t *clients = NULL;
while (true) {
maxSd = get_max_socket(&server, &clients);
if ((activity = select(maxSd + 1, &server.readfds,
NULL, NULL, NULL)) < 0
&& (errno != EINTR))
return (-1);
if (check_new_socket(&clients, &server, port) == -1)
return (-1);
receive_socket_message(&clients, &server);
}
destroy_clients(clients);
return (0);
}
謝謝你的幫助。
問題出在receive_socket_message
中:釋放列表元素時,不會將前一個節點鏈接到下一個節點。
這是修改后的版本:
static void receive_socket_message(ClientsList_t **clients,
MasterSocket_t *server)
{
ClientsList_t *temp = *clients;
ClientsList_t *tempDel = NULL;
ClientsList_t **link = clients;
int valread = 0;
int addrlen = 0;
char buffer[1025];
while (temp != NULL) {
if (FD_ISSET(temp->sockfd, &server->readfds)) {
if ((valread = read(temp->sockfd, buffer, sizeof(buffer))) == 0) {
tempDel = temp;
*link = temp = temp->next;
close(tempDel->sockfd);
free(tempDel);
continue;
} else {
buffer[valread] = '\0';
printf("%s\n", buffer);
}
}
link = &temp->next;
temp = temp->next;
}
}
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