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，任何帮助将不胜感激。
clang：错误：链接器命令失败，退出代码为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。为什么不编译？我把atomic_logger.c和atomic_logger.h放到与这个文件相同的文件夹中，以防万一，但我仍然得到这个错误。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，但我确信有一些明显的东西我不见了，因为我得到的错误信息是：
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)
先谢谢你帮助我解决这个问题......
答案 0 :(得分：2)
您永远不会告诉gcc编译atomic_logger.c或链接它。
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文件和链接它们一起用于最终输出二进制文件 - 所有这些都在一次调用中
另一种方法是使用.c开关将仅编译每个.o文件独立于其对应的-c文件。然后将链接所有.o文件放在一起作为输出二进制文件。
$ 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"与最终链接流程没有任何关系 - 它不会自动通知GCC查看atomic_logger.c。它只是复制+粘贴该头文件的内容在它所包含的位置。