Undefined reference to main - collect2 ld returned 1 exit status

Question

I m trying to compile a program  called es3   but  when I write from terminal   gcc es3 c -o es3  it appears this message    usr lib gcc i686-linux-gnu 4 4 5             lib crt1 o  In function   start     text 0x18   undefined reference to  main  collect2  ld returned 1 exit status   What could I do

User · Answer

In my case it was just because I had not Saved the source file and was trying to compile a empty file

User · Answer

Executable file needs a main function  See below hello world demo    include  lt stdio h gt  int main void            printf  Hello world  n            return 0      As you can see there is a main function  if you don t have this main function  ld will report  undefined reference to main      check my result     cat es3 c  include  lt stdio h gt  int main void        printf  Hello world  n        return 0      gcc -Wall -g -c es3 c   gcc -Wall -g es3 o -o es3      es3 Hello world     please use   objdump -t es3 o to check if there is a main symbol  Below is my result     objdump -t es3 o  es3 o      file format elf32-i386  SYMBOL TABLE  00000000 l    df  ABS   00000000 es3 c 00000000 l    d   text  00000000  text 00000000 l    d   data  00000000  data 00000000 l    d   bss   00000000  bss 00000000 l    d   debug abbrev  00000000  debug abbrev 00000000 l    d   debug info    00000000  debug info 00000000 l    d   debug line    00000000  debug line 00000000 l    d   rodata        00000000  rodata 00000000 l    d   debug frame   00000000  debug frame 00000000 l    d   debug loc     00000000  debug loc 00000000 l    d   debug pubnames        00000000  debug pubnames 00000000 l    d   debug aranges 00000000  debug aranges 00000000 l    d   debug str     00000000  debug str 00000000 l    d   note GNU-stack        00000000  note GNU-stack 00000000 l    d   comment       00000000  comment 00000000 g     F  text  0000002b main 00000000          UND   00000000 puts

User · Answer

I my case I found out the void for the main function declaration was missing    I was previously using Visual Studio in Windows and this was never a problem  so I thought I might leave it out now too

User · Answer

Perhaps your main function has been commented out because of e g  preprocessing  To learn what preprocessing is doing  try gcc -C -E es3 c  gt  es3 i then look with an editor into the generated file es3 i  and search main inside it    First  you should always  since you are a newbie  compile with    gcc -Wall -g -c es3 c   gcc -Wall -g es3 o -o es3   The -Wall flag is extremely important  and you should always use it  It tells the compiler to give you  almost  all warnings  And you should always listen to the warnings  i e  correct your source code file es3 C till you got no more warnings   The -g flag is important also  because it asks gcc to put debugging information in the object file and the executable  Then you are able to use a debugger  like gdb  to debug your program   To get the list of symbols in an object file or an executable  you can use nm   Of course  I m assuming you use a GNU Linux system  and I invite you to use GNU Linux if you don t use it already

User · Answer

It means that es3 c does not define a main function  and you are attempting to create an executable out of it  An executable needs to have an entry point  thereby the linker complains   To compile only to an object file  use the -c option   gcc es3 c -c gcc es3 o main c -o es3   The above compiles es3 c to an object file  then compiles a file main c that would contain the main function  and the linker merges es3 o and main o into an executable called es3

User · Answer

One possibility which has not been mentioned so far is that you might not be editing the file you think you are  i e  your editor might have a different cwd than you had in mind   Run  more  on the file you re compiling to double check that it does indeed have the contents you hope it does  Hope that helps

User · Answer

You can just add a main function to resolve this problem  Just like   int main         return 0

[c] Undefined reference to main - collect2: ld returned 1 exit status

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