C Linking Error undefined reference to main

Question

I have read the other answers on this topic  and unfortunately they have not helped me  I am attempting to link several c programs together  and I am getting an error in response     gcc -o runexp o scd o data proc o -lm -fopenmp  usr lib gcc x86 64-linux-gnu 4 6          x86 64-linux-gnu crt1 o  In function   start     text 0x20   undefined reference to  main  collect2  ld returned 1 exit status make     runexp  Error 1   I have exactly one main function and it is in runexp  The form is   int main void                  return 0      Any thoughts on why I might get this error  Thanks

User · Answer

You are overwriting your object file runexp o by running this command     gcc -o runexp o scd o data proc o -lm -fopenmp   In fact  the -o is for the output file  You need to run    gcc -o runexp out runexp o scd o data proc o -lm -fopenmp   runexp out will be you binary file

User · Answer

You should provide output file name after -o option  In your case runexp o is treated as output file name  not input object file and thus your main function is undefined

User · Answer

You re not including the C file that contains main   when compiling  so the linker isn t seeing it   You need to add it     gcc -o runexp runexp c scd o data proc o -lm -fopenmp

User · Answer

Generally you compile most  c files in the following way   gcc foo c -o foo  It might vary depending on what  includes you used or if you have any external  h files  Generally  when you have a C file  it looks somewhat like the following    include  lt stdio h gt         any other includes  prototypes  struct delcarations           int main           code        When I get an  undefined reference to main   it usually means that I have a  c file that does not have int main   in the file  If you first learned java  this is an understandable manner of confusion since in Java  your code usually looks like the following     any import statements you have public class Foo      int main          I would advise looking to see if you have int main   at the top

[c] C Linking Error: undefined reference to 'main'

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