nm (

name mangling In compiler construction, name mangling (also called name decoration) is a technique used to solve various problems caused by the need to resolve unique names for programming entities in many modern programming languages. It provides a way of e ...

) is a

Unix Unix (; trademarked as UNIX) is a family of multitasking, multiuser computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, and ot ...

command used to dump the

symbol table In computer science, a symbol table is a data structure used by a language translator such as a compiler or interpreter, where each identifier (or symbols), constants, procedures and functions in a program's source code is associated with info ...

and their attributes from a

binary Binary may refer to: Science and technology Mathematics * Binary number, a representation of numbers using only two digits (0 and 1) * Binary function, a function that takes two arguments * Binary operation, a mathematical operation that t ...

executable In computing, executable code, an executable file, or an executable program, sometimes simply referred to as an executable or binary, causes a computer "to perform indicated tasks according to encoded instruction (computer science), instructi ...

file (including

libraries A library is a collection of materials, books or media that are accessible for use and not just for display purposes. A library provides physical (hard copies) or digital access (soft copies) materials, and may be a physical location or a vir ...

, compiled object modules, shared-object files, and standalone

s). The output from nm distinguishes between various symbol types. For example, it differentiates between a

function Function or functionality may refer to: Computing * Function key, a type of key on computer keyboards * Function model, a structured representation of processes in a system * Function object or functor or functionoid, a concept of object-oriente ...

that is supplied by an object module and a function that is required by it. nm is used as an aid for

debugging In computer programming and software development, debugging is the process of finding and resolving '' bugs'' (defects or problems that prevent correct operation) within computer programs, software, or systems. Debugging tactics can involve in ...

, to help resolve problems arising from name conflicts and

C++ C++ (pronounced "C plus plus") is a high-level general-purpose programming language created by Danish computer scientist Bjarne Stroustrup as an extension of the C programming language, or "C with Classes". The language has expanded significan ...

name mangling, and to validate other parts of the

toolchain In software, a toolchain is a set of programming tools that is used to perform a complex software development task or to create a software product, which is typically another computer program or a set of related programs. In general, the tools form ...

. This command is shipped with a number of later versions of

and similar

operating system An operating system (OS) is system software that manages computer hardware, software resources, and provides common services for computer programs. Time-sharing operating systems schedule tasks for efficient use of the system and may also in ...

s including Plan 9. The

GNU Project The GNU Project () is a free software, mass collaboration project announced by Richard Stallman on September 27, 1983. Its goal is to give computer users freedom and control in their use of their computers and computing devices by collaborati ...

ships an implementation of nm as part of the

GNU Binutils The GNU Binary Utilities, or , are a set of programming tools for creating and managing binary programs, object files, libraries, profile data, and assembly source code. Tools They were originally written by programmers at Cygnus Solutions. ...

package.

nm output sample

/* * File name: test.c * For C code compile with: * gcc -c test.c * * For C++ code compile with: * g++ -c test.cpp */ int global_var; int global_var_init = 26; static int static_var; static int static_var_init = 25; static int static_function() int global_function(int p) int global_function2() #ifdef __cplusplus extern "C" #endif void non_mangled_function() int main(void) If the previous code is compiled with the gcc C compiler, the output of the nm command is the following: # nm test.o 0000000a T global_function 00000025 T global_function2 00000004 C global_var 00000000 D global_var_init 00000004 b local_static_var.1255 00000008 d local_static_var_init.1256 0000003b T main 00000036 T non_mangled_function 00000000 t static_function 00000000 b static_var 00000004 d static_var_init When the C++ compiler is used, the output differs: # nm test.o 0000000a T _Z15global_functioni 00000025 T _Z16global_function2v 00000004 b _ZL10static_var 00000000 t _ZL15static_functionv 00000004 d _ZL15static_var_init 00000008 b _ZZ15global_functioniE16local_static_var 00000008 d _ZZ15global_functioniE21local_static_var_init U __gxx_personality_v0 00000000 B global_var 00000000 D global_var_init 0000003b T main 00000036 T non_mangled_function The differences between the outputs also show an example of solving the name mangling problem by using

extern "C" The C and C++ programming languages are closely related but have many significant differences. C++ began as a fork of an early, pre-standardized C, and was designed to be mostly source-and-link compatible with C compilers of the time. Due to thi ...

in C++ code.

External links

* * Unix programming tools Unix SUS2008 utilities Articles with example C code Plan 9 commands {{unix-stub

nm output sample

See also

External links