Multiple definition of 'err _ sys & #39;, errsys

Multiple definition of 'err _ sys ', errsys

Address: http://www.cnblogs.com/yhLinux/p/4079930.html

 

Problem description:

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The codelist8-7.c uses the functions TELL_WAIT (), WAIT_PARENT (), and TELL_CHILD () in the codelist15-3.c when practicing the list of APUE programs in UNIX environment advanced programming ().

Codelist8-7.c:

1 # include "apue. h "2 3 static void charatatime (char *); 4 5 int main (void) 6 {7 pid_t pid; 8 TELL_WAIT (); 9 10 if (pid = fork () <0) {11 err_sys ("fork error"); 12} else if (pid = 0) {13 WAIT_PARENT (); /* parent goes first */14 charatatime ("output from child \ n"); 15} else {16 charatatime ("output from parent \ n "); 17 TELL_CHILD (pid); 18} 19 exit (0); 20} 21 22 static void charatatime (char * str) 23 {24 Char * ptr; 25 int c; 26 27 setbuf (stdout, NULL);/* set unbuffered */28 for (ptr = str; (c = * ptr ++ )! = 0;) 29 putc (c, stdout); 30}Codelist8-7.c

Codelist15-3.c:

1 # include "apue. h "2 3 static int pfd1 [2], pfd2 [2]; 4 5 void TELL_WAIT (void) 6 {7 if (pipe (pfd1) <0 | pipe (pfd2) <0) 8 err_sys ("pipe error"); 9} 10 11 void TELL_PARENT (pid_t pid) 12 {13 if (write (pfd2 [1], "c ", 1 )! = 1) 14 err_sys ("write error"); 15} 16 17 void WAIT_PARENT (void) 18 {19 char c; 20 21 if (read (pfd1 [0], & c, 1 )! = 1) 22 err_sys ("read error"); 23 24 if (c! = 'P') 25 err_quit ("WAIT_PARENT: incorrect data"); 26} 27 28 void TELL_CHILD (pid_t pid) 29 {30 if (write (pfd1 [1], "p", 1 )! = 1) 31 err_sys ("write error"); 32} 33 34 void WAIT_CHILD (void) 35 {36 char c; 37 38 if (read (pfd2 [0], & c, 1 )! = 1) 39 err_sys ("read error"); 40 41 if (c! = 'C') 42 err_quit ("WAIT_CHILD: incorrect data"); 43}View Code

When compiling 8-7 with the command, the following error is prompted:

$Gcc Codelist8-7.c codelist15-3.c-o 8-7/Tmp/ccMDAwpv. o: In function 'err _ ret ': codelist15-3.c :(. text + 0x0 ):Multiple definitionOf 'err _ ret '/tmp/ccXi2EPL. o: codelist8-7.c :(. text + 0x0): first defined here/tmp/ccMDAwpv. o: In function 'err _ sys ': codelist15-3.c :(. text + 0xa9): multiple definition of 'err _ sys '/tmp/ccXi2EPL. o: codelist8-7.c :(. text + 0xa9): first defined here/tmp/ccMDAwpv. o: In function 'err _ exit ': codelist15-3.c :(. text + 0x15a): multiple definition of 'err _ exit '/tmp/ccXi2EPL. o: codelist8-7.c :(. text + 0x15a): first defined here/tmp/ccMDAwpv. o: In function 'err _ dump ': codelist15-3.c :(. text + 0x209): multiple definition of 'err _ dump'/tmp/ccXi2EPL. o: codelist8-7.c :(. text + 0x209): first defined here/tmp/ccMDAwpv. o: In function 'err _ msg ': codelist15-3.c :(. text + 0x2b5): multiple definition of 'err _ msg '/tmp/ccXi2EPL. o: codelist8-7.c :(. text + 0x2b5): first defined here/tmp/ccMDAwpv. o: In function 'err _ quit ': codelist15-3.c :(. text + 0x360): multiple definition of 'err _ quit '/tmp/ccXi2EPL. o: codelist8-7.c :(. text + 0x360): first defined herecollect2: ld returns 1

Find the following online comments:

1. http://bbs.chinaunix.net/thread-3699788-1-1.html

I think it's because I am in apue. # include "error. c ", although apue. in h # ifndef _ APUE_H _ # define _ APUE_H _ copy the code, but the CompilerSeparate CompilationSo # include "apue. h" in the wait. c and 14.6.c files will contain two error. c files,
In the error. c file, it is the definition of the function (not Declaration. So I deleted it in apue. # include "error. c ", makefile file: inc =/home/lee/program/apue/apue.2e/include/error =/home/lee/program/apue/apue.2e/include/error. c. out: 14.6.c wait. c gcc-I $ (inc)-o. out 14.6.c wait. c $ (error) copy the code apue. the hfile is in the/home/lee/program/apue/apue.2d/include/directory. So there is no problem. I wonder if this is what I think.

# Yes, andDo not include c files if there is no sufficient reason

The above discussion has been well discussed. It turns out that I used to follow the method in this article [http://blog.csdn.net/quan9ing007/article/details/9929659this is not a problem.Apue. hAndError. hCopy/Usr/includeFolder.

In fact, according to the above statement, we should not put # include "error. c" in apue. h, andError. cPut in/Usr/includeDirectory, add error. c during each compilation.

 

Solution (recommended):

ThereforeApue. hPut it in the/usr/include directory, andError. c is often used., We will defineError environment variableIn this way, you do not have to copy error. c to the relevant folder every time for compilation.

Assume that the current user is Lee and error. c is stored in/home/Lee/code_Lee/APUE/part_of_source /:

Sudo cp/home/Lee/code_Lee/APUE/part_of_source/apue. h/usr/include/apue. hsudo chmod a + r/usr/include/apue. hvi/home/Lee /. bashrc in. added the apue_error variable at the end of bashrc: apue_error =/home/Lee/code_Lee/APUE/part_of_source/error. csource ~ /. Bashrc/* this is very important. Be sure to execute */echo$ {Apue_error}/Home/Lee/code_Lee/APUE/part_of_source/error. cgcc codelist8-6.c $ {apue_error}-o 8-6 success! Gcc codelist8-7.c codelist15-3.c $ {apue_error}-o 8-7 successful !!

 

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References:

1. Linux environment variables

Http://www.cnblogs.com/Neddy/archive/2011/03/01/1968018.html

2. linux environment variables ()

Http://www.cnblogs.com/growup/archive/2011/07/02/2096142.html

Makefile Compilation: multiple definition

There is a RMB _chk_str in RMB. o that is repeated with the definition in your testRMB. o. Check which definition is wrong.

The strange thing in makefile is: $ CC $ (LIBFLAGS) $? -O $ @ $ (LIBS1), change it to the following:
$ CC $? -O $ @ $ (LIBFLAGS) $ (LIBS1)

Multiple definition of 'main' in C Language'

Are you defining the main function in other files of the same project? If yes, It must be wrong;

A project can only have one main function. You can change the name of the main function in other files.