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><A
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>Checking if a Library Provides a Function</A
></H1
><P
>A linker, any linker, knits together object files (some of which may be in libraries) such that every function needed by the program has a definition.  If the linker fails to locate a definition for even one function, it will fail and the program will not run.  </P
><P
>Returning to <A
HREF="rtl.htm#BSQLDB.UNRESOLVED"
><TT
CLASS="FILENAME"
>bsqldb.o</TT
></A
>, we can use <B
CLASS="COMMAND"
>nm</B
> to see which functions are unresolved, and determine whether or not a particular library contains them.  We'll ignore the symbols that start with an underscore, marking them per the C standard as being provided by the implementation<A
NAME="AEN6494"
HREF="#FTN.AEN6494"
><SPAN
CLASS="footnote"
>[1]</SPAN
></A
>, and focus on the last five in this abbreviated list.  

 <P
></P
><DIV
CLASS="VARIABLELIST"
><P
><B
>Some unresolved functions in <TT
CLASS="FILENAME"
>bsqldb.o</TT
></B
></P
><DL
><DT
><CODE
CLASS="FUNCTION"
>asprintf</CODE
>, <CODE
CLASS="FUNCTION"
>basename</CODE
></DT
><DD
><P
>Normally provided by the standard C library, but if not by <SPAN
CLASS="PRODUCTNAME"
>FreeTDS</SPAN
>'s replacements library: 
<PRE
CLASS="SCREEN"
><SAMP
CLASS="PROMPT"
>$ </SAMP
><KBD
CLASS="USERINPUT"
>nm /usr/lib/libc.a | grep -w T | grep -E 'asprintf|basename'</KBD
>
<SAMP
CLASS="COMPUTEROUTPUT"
>0000000000000000 T _basename
0000000000000000 T _asprintf</SAMP
></PRE
>
			</P
></DD
><DT
><CODE
CLASS="FUNCTION"
>calloc</CODE
></DT
><DD
><P
>Provided by the standard C library:
<PRE
CLASS="SCREEN"
><SAMP
CLASS="PROMPT"
>$ </SAMP
><KBD
CLASS="USERINPUT"
>nm /usr/lib/libc.a | grep -w T | grep calloc </KBD
>
<SAMP
CLASS="COMPUTEROUTPUT"
>0000000000004240 T calloc</SAMP
></PRE
>
			</P
></DD
><DT
><CODE
CLASS="FUNCTION"
>dbaltbind</CODE
>, <CODE
CLASS="FUNCTION"
>dbaltcolid</CODE
></DT
><DD
><P
>Provided by <SPAN
CLASS="SYSTEMITEM"
>DB-Library</SPAN
>:
<PRE
CLASS="SCREEN"
><SAMP
CLASS="PROMPT"
>$ </SAMP
><KBD
CLASS="USERINPUT"
>nm libsybdb.a | grep -Ew 'dbaltbind|dbaltcolid'</KBD
>
<SAMP
CLASS="COMPUTEROUTPUT"
>0000000000007140 T dbaltbind
0000000000003590 T dbaltcolid</SAMP
></PRE
>
			</P
></DD
></DL
></DIV
>

Although these examples refer to static libraries, <B
CLASS="COMMAND"
>nm</B
> works just as well with dynamic libraries, too.  </P
><P
>There are other tools besides <B
CLASS="COMMAND"
>nm</B
>.  Windows&reg;, for instance, has <B
CLASS="COMMAND"
>dumpbin</B
>, and the GNU bintools include <B
CLASS="COMMAND"
>objdump</B
>.  </P
></DIV
><H3
CLASS="FOOTNOTES"
>Notes</H3
><TABLE
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><A
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><SPAN
CLASS="footnote"
>[1]</SPAN
></A
></TD
><TD
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><P
>Why and how leading underscores enter into this discussion is just one more example of arcane historical practices one needs to know to master the subject.  For our purposes, though, it's enough to know that <SPAN
CLASS="QUOTE"
>"implementation-provided"</SPAN
> functions like these &mdash; functions provided by the C standard library &mdash; often have an underscored prepended.  </P
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