c - 试图使原子日志记录工作

Question

我一直收到这个错误，我不知道为什么。我正在努力使这项工作失去理智，我们将不胜感激任何帮助。

clang: error: linker command failed with exit code 1

代码:

1 #include <stdio.h>
2 #include <stdlib.h>
3 #include <string.h>
4 #include <unistd.h>
5 #include "atomic_logger.h"
6 
7 #define BUFSIZE 1024
8 
9 int main  (int argc, char *argv[]) {
10    char buf[BUFSIZE];
11    pid_t childpid = 0;
12    int i, n;
13 
14    if (argc != 3){       /* check for valid number of command-line arguments */
15       fprintf (stderr, "Usage: %s processes filename\n", argv[0]);
16       return 1;
17    }
18    n = atoi(argv[1]);                              /* create a process chain */
19    for (i = 1; i < n; i++)
20        if ((childpid = fork()))
21           break;
22    if (childpid == -1) {
23       perror("Failed to fork");
24       return 1;
25    }
26 
27    if (atomic_log_open(argv[2]) == -1) {             /* open atomic log file */
28       fprintf(stderr, "Failed to open log file");
29       return 1;
30    }
31                                 /* log the output, using two different forms */
32    atomic_log_printf("i:%d process:%ld", i, (long)getpid());
33 
34    atomic_log_printf(" parent:%ld child:%ld\n", (long)getppid(), (long)childpid);
35 
36 
37    if (atomic_log_send() == -1) {
38       fprintf(stderr, "Failed to send to log file");
39       return 1;
40    }
41    atomic_log_close();
42    return 0;
43 }

是的，这是学校作业的一部分，但我不需要帮助编码，我需要帮助编译。为什么这不会编译？我将 atomic_logger.c 和 atomic_logger.h 放入与该文件相同的文件夹中，以防万一，但我仍然收到此错误。出了什么问题？ atomic_logger.h如下:

  1 int atomic_log_array(char *s, int len);
  2 int atomic_log_clear();
  3 int atomic_log_close();
  4 int atomic_log_open(char *fn);
  5 int atomic_log_printf(char *fmt, ...);
  6 int atomic_log_send();
  7 int atomic_log_string(char *s);

和atomic_logger.c如下:

  1 #include <errno.h>
  2 #include <fcntl.h>
  3 #include <stdarg.h>
  4 #include <stdio.h>
  5 #include <stdlib.h>
  6 #include <string.h>
  7 #include <unistd.h>
  8 #include <sys/stat.h>
  9 
 10 #define FILE_PERMS (S_IRUSR | S_IWUSR| S_IRGRP | S_IROTH)
 11 #define OPEN_FLAGS (O_WRONLY|O_APPEND|O_CREAT)
 12 typedef struct list {
 13    char *entry;
 14    int len;
 15    struct list *next;
 16 } list;
 17 
 18 static int fd = -1;
 19 static list *first = NULL;
 20 static list *last = NULL;
 21 
 22 
 23 /* -----------------------------------------------------------------
 24    Private Functions
 25 */
 26 
 27 /* This is the same as write, but restarts if interrupted by a signal */
 28 static ssize_t my_write(int fd, void *buf, size_t size) {
 29    ssize_t bytes;
 30 
 31    while (((bytes = write(fd, buf, size)) == -1) && (errno == EINTR));
 32    return bytes;
 33 }
 34 
 35 /* Insert an entry with the given len field, but allocate extra bytes.*/
 36 /* Return a pointer to the new entry on success or NULL on failure.   */
 37 static list *insert_new_entry(int len, int extra) {
 38    char *new_str;
 39    list *new_entry;
 40 
 41    new_entry = (list *)malloc(sizeof(list)+len+extra);
 42    if (new_entry == NULL)
 43       return NULL;
 44    new_str = (char *)new_entry+sizeof(list);
 45    new_entry->entry = new_str;
 46    new_entry->next = NULL;
 47    new_entry->len = len;
 48    if (last == NULL)
 49       first = new_entry;
 50    else
 51       last->next = new_entry;
 52    last = new_entry;
 53    return new_entry;
 54 }
 55 
 56 /* Return the sum of the lengths of all the entries.                  */
 57 static int get_length() {
 58    int len = 0;
 59    list *current;
 60 
 61    current = first;
 62    while (current != NULL) {
 63       len += current->len;
 64       current = current->next;
 65    }
 66    return len;
 67 }
 68 
 69 /* Clear the list and free all the space.                             */
 70 static void clear() {
 71    list *current;
 72    list *free_entry;
 73 
 74    current = first;
 75    while (current != NULL) {
 76       free_entry = current;
 77       current = current->next;
 78       free(free_entry);
 79    }
 80    first = NULL;
 81    last = NULL;
 82 }
 83 
 84 /* -----------------------------------------------------------------
 85    Public Functions
 86 */
 87 
 88 /* Open the given file for logging.                                   */
 89 /* If successful, return 0.  Otherwise, return -1 with errno set.     */
 90 int atomic_log_open(char *fn) {
 91    while (fd = open(fn, OPEN_FLAGS, FILE_PERMS), fd == -1 && errno == EINTR);
 92    if (fd < 0)
 93       return -1;
 94    return 0;
 95 }
 96 
 97 /* Insert the given array with given size in the list.                */
 98 /* If successful, return 0.  Otherwise, return -1 with errno set.     */
 99 int atomic_log_array(char *s, int len) {
100    list *new_entry;
100    list *new_entry;
101 
102    if (fd < 0) {
103       errno = EINVAL;
104       return -1;
105    }
106    new_entry = insert_new_entry(len, 0);
107    if (new_entry == NULL)
108       return -1;
109    (void)memcpy(new_entry->entry, s, len);
110    return 0;
111 }
112 
113 /* Insert the given string in the list.                               */
114 /* Do not include the string terminator.                              */
115 /* If successful, return 0.  Otherwise, return -1 with errno set.     */
116 int atomic_log_string(char *s) {
117    return atomic_log_array(s, strlen(s));
118 }
119 
120 /* Insert an entry in the list.                                       */
121 /* The syntax is similar to printf.                                   */
122 /* Include the string terminator but do not count it in the length.   */
123 /* If successful, return 0.  Otherwise, return -1 with errno set.     */
124 int atomic_log_printf(char *fmt, ...) {
125    va_list ap;
126    char ch;
127    int len;
128    list *new_entry;
129 
130    if (fd < 0) {
131       errno = EINVAL;
132       return -1;
133    }
134    va_start(ap, fmt);
135    len = vsnprintf(&ch, 1, fmt, ap);
136    new_entry = insert_new_entry(len, 1);
137    if (new_entry == NULL)
138       return -1;
139    vsprintf(new_entry->entry, fmt, ap);
140    return 0;
141 }
142 
143 /* Attempt to log the entire list with a single write.                */
144 /* Clear the list if successful.                                      */
145 /* If successful, return 0.  Otherwise, return -1 with errno set.     */
146 /* If the entire list cannot be logged with a single write, this is   */ 
147 /*   considered a failure.                                            */ 
148 int atomic_log_send() { 
149    char *buf; 
150    list *current; 
151    int len; 
152  
153    if (fd < 0) { 
154       errno = EINVAL; 
155       return -1; 
156    } 
157    len = get_length(); 
158    if (len == 0) 
159       return 0; 
160    buf = (char *)malloc(len); 
161    if (buf == NULL) 
162       return -1; 
163    current = first; 
164    len = 0; 
165    while (current != NULL) { 
166       (void)memcpy(buf+len, current->entry, current->len); 
167       len += current->len; 
168       current = current->next; 
169    } 
170    if (my_write(fd, buf, len) != len) { 
171       free(buf); 
172       errno = EAGAIN; 
173       return -1; 
174    } 
175    free(buf); 
176    clear(); 
177    return 0; 
178 } 
179  
180 /* Clear the list and free all the space without logging anything.    */ 
181 int atomic_log_clear() { 
182    clear(); 
183    return 0; 
184 } 
185  
186 /* Close the log file.  Any data not yet logged is lost.              */ 
187 int atomic_log_close() { 
188    int retval; 
189    clear(); 
190    while (retval = close(fd), retval == -1 && errno == EINTR) ; 
191    return retval; 
192 }

事情看起来对我来说是正确的，但我确信我遗漏了一些明显的东西，因为我收到的错误消息是:

imacbook:lab4 smythe1$ gcc -o ex8/chainforkopenlog ex8/chainforkopenlog.c 
Undefined symbols for architecture x86_64:
  "_atomic_log_close", referenced from:
      _main in chainforkopenlog-44aa15.o
  "_atomic_log_open", referenced from:
      _main in chainforkopenlog-44aa15.o
  "_atomic_log_printf", referenced from:
      _main in chainforkopenlog-44aa15.o
  "_atomic_log_send", referenced from:
      _main in chainforkopenlog-44aa15.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

在此先感谢您帮助我解决此问题...

Answer 1

你永远不会说gcc编译atomic_logger.c ，或针对它的链接。

最简单的补救措施是

$ gcc -o ex8/chainforkopenlog ex8/chainforkopenlog.c ex8/atomic_logger.c 

这告诉gcc 编译所有列出的.c文件并将它们链接在一起以获得最终输出二进制文件 - 所有这些都在一次调用中完成。

另一种方法是只编译每个.c独立于其对应的文件 .o使用 -c 的文件转变。然后链接所有.o文件一起用于输出二进制文件。

$ gcc -c ex8/chainforkopenlog.c       # Produces chainforkopenlog.o
$ gcc -c ex8/atomic_logger.c          # Produces atomic_logger.o

$ gcc -o ex8/chainforkopenlog chainforkopenlog.o atomic_logger.o

请注意 #include "atomic_logger.h"与最终链接过程没有任何关系——它不会自动通知 GCC 查看 atomic_logger.c .它只是将该头文件的内容复制并粘贴到包含它的位置。