使用Makefile后出现未定义的参考错误

Question

I wrote a makefile to link all the .c files that i wanted to.But then again i get errors of undefined reference.The code for the makefile is:

FILES.o=set.o hash.o nfa.o printnfa.o input.o terp.o dfa.o minimize.o defnext.o print_ar.o pairs.o squash.o print.o assort.o prnt.o printv.o bintoasc.o ferr.o onferr.o fputstr.o pchar.o driver.o searchenv.o hashadd.o 

PROGRAM= lexer

all: ${PROGRAM}

${PROGRAM}: ${FILES.o}
${CC} -o $@ ${CFLAGS} $^ ${LDFLAGS} ${LDLIBS}

But still it leads to undefined errors like :

/usr/lib/gcc/x86_64-linux-gnu/4.7/../../../x86_64-linux-gnu/crt1.o: In function   `_start':(.text+0x20): undefined reference to `main'
nfa.o: In function `parse_err':
nfa.c:(.text+0x21): undefined reference to `Actual_lineno'
nfa.o: In function `save':
nfa.c:(.text+0x2d1): undefined reference to `Lineno'  
nfa.o: In function `advance':
nfa.c:(.text+0x8b4): undefined reference to `esc'
nfa.o: In function `rule':
nfa.c:(.text+0xae1): undefined reference to `Unix'
nfa.o: In function `term':
nfa.c:(.text+0xfbd): undefined reference to `Unix'
nfa.c:(.text+0x10a2): undefined reference to `Unix'
nfa.o: In function `thompson':
nfa.c:(.text+0x1355): undefined reference to `CLEAR_STACK'
nfa.c:(.text+0x13ab): undefined reference to `Verbose'
nfa.c:(.text+0x13d3): undefined reference to `printf_nfa'
nfa.c:(.text+0x13d9): undefined reference to `Verbose'
input.o: In function `get_expr':
input.c:(.text+0x13): undefined reference to `Input_buf'
input.c:(.text+0x20): undefined reference to `Verbose'
input.c:(.text+0x2b): undefined reference to `Actual_lineno'
input.c:(.text+0x52): undefined reference to `Actual_lineno'
input.c:(.text+0x7a): undefined reference to `Actual_lineno'
input.c:(.text+0x83): undefined reference to `Actual_lineno'
input.c:(.text+0x8a): undefined reference to `Input_buf'
input.c:(.text+0x93): undefined reference to `Input_buf'
input.c:(.text+0xe2): undefined reference to `Ifile'
input.c:(.text+0x10c): undefined reference to `Verbose'
input.c:(.text+0x11c): undefined reference to `Input_buf'
input.c:(.text+0x136): undefined reference to `Input_buf'
dfa.o: In function `dfa':
dfa.c:(.text+0x69): undefined reference to `Verbose'
dfa.c:(.text+0x1c6): undefined reference to `Verbose'
dfa.c:(.text+0x215): undefined reference to `Verbose'
dfa.o: In function `get_unmarked':
dfa.c:(.text+0x3a8): undefined reference to `Verbose'
minimize.o: In function `init_groups':
minimize.c:(.text+0x28c): undefined reference to `Verbose'
minimize.o:minimize.c:(.text+0x550): more undefined references to `Verbose' follow
print.o: In function `pdriver': 
print.c:(.text+0x483): undefined reference to `No_lines' 
print.c:(.text+0x4eb): undefined reference to `No_lines'
print.c:(.text+0x4f6): undefined reference to `Input_file_name'  
print.c:(.text+0x585): undefined reference to `No_lines'
collect2: error: ld returned 1 exit status
make: *** [lexer] Error 1

All the undefined references are however present in 2 header files :1.stack.h 2.global.h..Still the errors.please help!

The global.h file i am using is:

#ifndef __GLOBAL_H 
#define __GLOBAL_H
#include <stdio.h>

#ifdef ALLOC
#   define CLASS
#   define I(x) x
#else
#   define CLASS extern
#   define I(x)
#endif
#define MAXINP 2048

CLASS int Verbose   I(=0);
CLASS int No_lines  I(=0);
CLASS int Unix      I(=0);
CLASS int Public    I(=0);
CLASS char *Template    I(="lex.par");
CLASS int Actual_lineno I(=1);
CLASS int Lineno    I(=1);

CLASS char Input_buf[MAXINP];   //line buffer for input
CLASS char *Input_file_name;    //Input file name
CLASS FILE *Ifile;      //Input Stream
CLASS FILE *ofile;      //Output Stream

#endif

Answer 1

Your problem isn't related to the Makefile per se. The header-only include file global.h contains declarations of variables. These declarations have to be turned into actual definitions in one compilation unit, so that they have space for them allocated in one of your object files.

The way your header file is designed, the definition of the variable ALLOC determines whether the variables are just declared or defined.

The regular include without ALLOC yields for example:

extern int Verbose;

The extern keyword indicates that the variable Verbose is not defined. No memory is allocated for it (and it therefore can't have an initialiser) and that it is probably defined in another object file.

When ALLOC is defined, the declaration becomes a definition with initialisation:

int Verbose = 0;

Pick one of the files that include global.h and define ALLOC before including it, for example:

input.c

#define ALLOC
#include "global.h"

You should then have the symbol Verbose defined as an int with initial value 0 in global.o :

> nm input.o | grep Verbose
0000000000000000 B Verbose
> nm set.o | grep Verbose
                 U Verbose

( nm is a Linux utility that lists the symbols in an object file. Windows has dumpbin .)

The U in the object file without ALLOC means that the symbol is undefined, ie referenced but not defined in this object file. The B in input.o denotes the section where the symol is defined. When you link, you can have many U s, but for each symbol that is undefined in an object file, you also need one object file where the symbol is defined.

Answer 2

您应该在makefile中包含的所有文件中添加头文件...否则这些文件将无法识别这些变量