7_13发现了一个小问题为啥在do_line函数里赋值语句在变量定义语句之前就会报错？

来源：互联网发布：三菱fx2n pid编程手册编辑：程序博客网时间：2024/05/29 17:06

1.在变量定义之前出错：

<bldc:/home/tingbinz/apue.3e/SBSCODE/7>R*_*G:vim 7_13.c
1 #include "apue.h"
2 #include <setjmp.h>
3 #define TOKEN 5
4 void do_line (char *ptr);
5 void cmd_add (void);
6 int get_token(void);
7 #define MAXLINE 1024
8
9 jmp_buf jmpbuffer;
10
11 int main()
12 {
13 char line[MAXLINE];
14 if (setjmp(jmpbuffer) != 0)
15 printf("error");
16 while (fgets(line,MAXLINE,stdin) != NULL){
17 do_line(line);
18 }
19 exit(0);
20 }
21
22 char *tok_ptr;
23
24 void do_line(char *ptr)
25 {
26 //tok_ptr = ptr;
27 tok_ptr = ptr;
28 int cmd;
29
30 //tok_ptr = ptr;
31 while ( (cmd = get_token()) > 0){
32 switch (cmd){
33 case TOKEN:
34 cmd_add();
35 break;
36 }
37 }
38
39 }
40
41 int get_token(void)
42 {
43 /* fetch the next token from the line pointed to by tok_ptr;*/
44 }
45
46 void cmd_add(void)
47 {
"7_13.c" 53L, 761C written
<bldc:/home/tingbinz/apue.3e/SBSCODE/7>R*_*G:gcc -Wall -ggdb3 setlongjmp 7_13.c
gcc: setlongjmp: No such file or directory
7_13.c:7: warning: `MAXLINE' redefined
apue.h:29: warning: this is the location of the previous definition
In file included from apue.h:132,
from 7_13.c:1:
error.c: In function `err_doit':
error.c:121: warning: implicit declaration of function `vsnprintf'
error.c:123: warning: implicit declaration of function `snprintf'
7_13.c: In function `do_line':
7_13.c:28: parse error before `int'
7_13.c:31: `cmd' undeclared (first use in this function)
7_13.c:31: (Each undeclared identifier is reported only once
7_13.c:31: for each function it appears in.)
7_13.c:34: warning: unreachable code at beginning of switch statement
7_13.c: In function `get_token':
7_13.c:44: warning: control reaches end of non-void function

挪到变量定义之后不再出错。
<bldc:/home/tingbinz/apue.3e/SBSCODE/7>R*_*G:vim 7_13.c
1 #include "apue.h"
2 #include <setjmp.h>
3 #define TOKEN 5
4 void do_line (char *ptr);
5 void cmd_add (void);
6 int get_token(void);
7 #define MAXLINE 1024
8
9 jmp_buf jmpbuffer;
10
11 int main()
12 {
13 char line[MAXLINE];
14 if (setjmp(jmpbuffer) != 0)
15 printf("error");
16 while (fgets(line,MAXLINE,stdin) != NULL){
17 do_line(line);
18 }
19 exit(0);
20 }
21
22 char *tok_ptr;
23
24 void do_line(char *ptr)
25 {
26 //tok_ptr = ptr;
27 int cmd;
28
29 tok_ptr = ptr;
30 while ( (cmd = get_token()) > 0){
31 switch (cmd){
32 case TOKEN:
33 cmd_add();
34 break;
35 }
36 }
37
38 }
39
40 int get_token(void)
41 {
42 /* fetch the next token from the line pointed to by tok_ptr;*/
43 }
44
45 void cmd_add(void)
46 {
47 int token;
"7_13.c" 52L, 743C written
<bldc:/home/tingbinz/apue.3e/SBSCODE/7>R*_*G:gcc -Wall -ggdb3 setlongjmp 7_13.c
gcc: setlongjmp: No such file or directory
7_13.c:7: warning: `MAXLINE' redefined
apue.h:29: warning: this is the location of the previous definition
In file included from apue.h:132,
from 7_13.c:1:
error.c: In function `err_doit':
error.c:121: warning: implicit declaration of function `vsnprintf'
error.c:123: warning: implicit declaration of function `snprintf'
7_13.c: In function `get_token':
7_13.c:43: warning: control reaches end of non-void function

求解释。

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