Undefined reference to sqrt or other mathematical functions

Question

I have this simple code   max    int  sqrt  number     and in the header I have    include  lt math h gt    But application still says undefined reference to sqrt  Do you see any problem here  It looks like everything should be okay

User · Answer

I had the same issue  but I simply solved it by adding -lm after the command that runs my code  Example   gcc code c -lm

User · Answer

Just adding the  include  lt math h gt  in c source file and -lm  in Makefile at the end will work for me       gcc -pthread -o p3 p3 c -lm

User · Answer

I suppose you have imported math h with  include  lt math h gt   So the only other reason I can see is a missing linking information  You must link your code with the -lm option   If you re simply trying to compile one file with gcc  just add -lm to your command line  otherwise  give some informations about your building process

User · Answer

You may find that you have to link with the math libraries on whatever system you re using  something like  gcc -o myprog myprog c -L path to libs -lm                                            - this bit here   Including headers lets a compiler know about function declarations but it does not necessarily automatically link to the code required to perform that function  Failing that  you ll need to show us your code  your compile command and the platform you re running on  operating system  compiler  etc   The following code compiles and links fine   include  lt math h gt  int main  void        int max   sqrt  9       return 0      Just be aware that some compilation systems depend on the order in which libraries are given on the command line  By that  I mean they may process the libraries in sequence and only use them to satisfy unresolved symbols at that point in the sequence  So  for example  given the commands  gcc -o plugh plugh o -lxyzzy gcc -o plugh -lxyzzy plugh o  and plugh o requires something from the xyzzy library  the second may not work as you expect  At the point where you list the library  there are no unresolved symbols to satisfy  And when the unresolved symbols from plugh o do appear  it s too late

User · Answer

Here are my observation  firstly you need to include the header math h as sqrt   function declared in math h header file  For e g   include  lt math h gt    secondly  if you read manual page of sqrt you will notice this line Link with -lm    include  lt math h gt     header file you need to include     double sqrt double x      prototype of sqrt   function     Link with -lm     Library linking instruction         But application still says undefined reference to sqrt  Do you see any   problem here     Compiler error is correct as you haven t linked your program with library lm  amp  linker is unable to find reference of sqrt    you need to link it explicitly  For e g  gcc -Wall -Wextra -Werror -pedantic test c -lm

[c] Undefined reference to sqrt (or other mathematical functions)

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