gcc link external library

Code:

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[b12573@iptel7] __linux_build_tmp $ gcc -o test test.c libMGCL.a -Wall
test.c: In function `main':
test.c:8: warning: implicit declaration of function `yyparse'
/usr/bin/ld: libMGCL.a(MGCL_parser.o): Relocations in generic ELF (EM: 20)
libMGCL.a: could not read symbols: File in wrong format
collect2: ld returned 1 exit status

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I get this error when I try to compile a .c source

test.c

Code:

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#include <stdio.h>


int main()
{
        printf("Hello world\n");

        yyparse();

        return 0;
}

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the yyparse() is a function from libMGCL.a

Where do I go wrong? I don't know very much about linking libraries and such!

Try including the necessary header file for the function.

> libMGCL.a: could not read symbols: File in wrong format
This is your first big problem, where did you get that library from?

To search a library, the command syntax would be
gcc -o test test.c -L. -lMGCL -Wall
The -L tells the linker where to look for more libraries
The -l tells the linker the name of a library, in this case libMGCL.a


Oh, and avoid calling your programs 'test', because there is a standard command called 'test' which appears to do nothing if you don't supply any command line parameters to it.

is there any tool for showing me the content of a library ? some info's about it or anything ?

The 'ar' tool will list the members of the library.
The 'nm' tool will list all the symbols in a library / object file / executable.

The command file might tell you what type of library that is.

Quote:

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Oh, and avoid calling your programs 'test', because there is a standard command called 'test' which appears to do nothing if you don't supply any command line parameters to it.

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It's a bash builtin, and it never prints anything no matter what, apparently.

Code:

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$ help test
test: test [expr]
    Exits with a status of 0 (true) or 1 (false) depending on
    the evaluation of EXPR.  Expressions may be unary or binary.  Unary
    expressions are often used to examine the status of a file.  There
    are string operators as well, and numeric comparison operators.

    File operators:

        -a FILE        True if file exists.
        -b FILE        True if file is block special.
        -c FILE        True if file is character special.
        -d FILE        True if file is a directory.
        -e FILE        True if file exists.
        -f FILE        True if file exists and is a regular file.
        -g FILE        True if file is set-group-id.
        -h FILE        True if file is a symbolic link.
        -L FILE        True if file is a symbolic link.
        -k FILE        True if file has its `sticky' bit set.
        -p FILE        True if file is a named pipe.
        -r FILE        True if file is readable by you.
        -s FILE        True if file exists and is not empty.
        -S FILE        True if file is a socket.
        -t FD          True if FD is opened on a terminal.
        -u FILE        True if the file is set-user-id.
        -w FILE        True if the file is writable by you.
        -x FILE        True if the file is executable by you.
        -O FILE        True if the file is effectively owned by you.
        -G FILE        True if the file is effectively owned by your group.
        -N FILE        True if the file has been modified since it was last read.

      FILE1 -nt FILE2  True if file1 is newer than file2 (according to
                      modification date).

      FILE1 -ot FILE2  True if file1 is older than file2.

      FILE1 -ef FILE2  True if file1 is a hard link to file2.

    String operators:

        -z STRING      True if string is empty.

        -n STRING
        STRING        True if string is not empty.

        STRING1 = STRING2
                      True if the strings are equal.
        STRING1 != STRING2
                      True if the strings are not equal.
        STRING1 < STRING2
                      True if STRING1 sorts before STRING2 lexicographically.
        STRING1 > STRING2
                      True if STRING1 sorts after STRING2 lexicographically.

    Other operators:

        -o OPTION      True if the shell option OPTION is enabled.
        ! EXPR        True if expr is false.
        EXPR1 -a EXPR2 True if both expr1 AND expr2 are true.
        EXPR1 -o EXPR2 True if either expr1 OR expr2 is true.

        arg1 OP arg2  Arithmetic tests.  OP is one of -eq, -ne,
                      -lt, -le, -gt, or -ge.

    Arithmetic binary operators return true if ARG1 is equal, not-equal,
    less-than, less-than-or-equal, greater-than, or greater-than-or-equal
    than ARG2.
$

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Quote:

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Originally Posted by Salem

To search a library, the command syntax would be
gcc -o test test.c -L. -lMGCL -Wall
The -L tells the linker where to look for more libraries
The -l tells the linker the name of a library, in this case libMGCL.a

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Listing the .a file directly on the link line is also perfectly legitimate.