Linker Error C undefined reference

Question

Possible Duplicate  What is an undefined reference unresolved external symbol error and how do I fix it    Trying to compile my program via g   -o prog1 main cpp -std c  0x I get the error   tmp cc1pZ8OM o  In function  main   main cpp   text 0x148   undefined reference to  Hash  insert int  char   collect2  error  ld returned 1 exit status  main cpp  include  lt iostream gt   include  lt cstring gt   include  lt cstdlib gt   include  lt cstdio gt   include  lt functional gt   include  quot Hash h quot   using namespace std   int main int argc  char  argv        preset prime number  int prime   101  hash lt char gt  h1  int key  Hash HashTable      check for Request  amp  string parameters if argc    3        cout  lt  lt   quot Run program with 2 parameters   Lower Case  quot   lt  lt  endl      cout  lt  lt   quot  1  insert  find  or delete quot   lt  lt  endl      cout  lt  lt   quot  2  string quot   lt  lt  endl     if strcmp argv 1    quot insert quot      0          Get Hash for argv 2  aka value     key   h1  argv 2           check 1     cout  lt  lt   quot Hash   quot   lt  lt  key  lt  lt  endl       key   key   prime         check 2     cout  lt  lt   quot Mod 101 Hash   quot   lt  lt  key  lt  lt  endl       HashTable insert key   argv 2      PROBLEM here     return 0     Hash h file   include  lt iostream gt   include  lt cstring gt   include  quot LinkedList h quot  using namespace std   class Hash     100 slot array for hash function LinkedList  hashFN 100    public  void insert int key  char value     void deleteItem int key     char  find int key         Any ideas  Using this to build a hash table with set size  Edit  Hash cpp file  include  lt iostream gt   include  lt cstring gt   include  quot Hash h quot   using namespace std   void Hash  insert int key  char value    hashFN key - gt addFront value   cout  lt  lt   quot Success  quot   lt  lt  endl      Trying to compile via terminal now with   g   -c Hash cpp -o Hash o g   -o prog1 main cpp Hash o -std c  0x  It goes into an infinite loop somehow

User · Answer

Your error shows you are not compiling file with the definition of the insert function  Update your command to include the file which contains the definition of that function and it should work

User · Answer

Your header file Hash h declares  what class hash should look like   but not its implementation  which is  presumably  in some other source file we ll call Hash cpp  By including the header in your main file  the compiler is informed of the description of class Hash when compiling the file  but not how class Hash actually works  When the linker tries to create the entire program  it then complains that the implementation  toHash  insert int  char   cannot be found   The solution is to link all the files together when creating the actual program binary  When using the g   frontend  you can do this by specifying all the source files together on the command line  For example   g   -o main Hash cpp main cpp   will create the main program called  main

User · Answer

This error tells you everything      undefined reference toHash  insert int  char    You re not linking with the implementations of functions defined in Hash h  Don t you have a Hash cpp to also compile and link

[c++] Linker Error C++ "undefined reference "

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