error linking crt1.o when running make

[zolo]

Hi,

I have run into a problem with a make file on Ubuntu 16.04 although I am not sure this is Linux distro dependent. Anyways I have a clas.h a clas.cpp and a main.cpp witch has the int main(int argc, char* argv[]). g++ -std=c++11 -fpermissive class.cpp main.cpp -o main works like charm and produces the executable and program works very well. Now I wrote an easy makefile (I thought in the beginning it is easy.)

all:main

main: clas.o
g++ -g -std=c++11 -Wall -fpermissive -o main clas.o

clas.o: clas.cpp clas.h
g++ -g -std=c++11 -Wall -fpermissive -c clas.cpp

Now this gives me an error and no executable is produced:
/usr/lib/gcc/x86_64-linux-gnu/5/../../../x86_64-linux-gnu/crt1.o: In function `_start':
(.text+0x20): undefined reference to `main'

Why do I need to link crt1.o? How do I get rid of this error?

Thanks

[Peter87]

You forgot about main.o. You need to add a target for it and use it in the main target like you do with clas.o.

[zolo]

cheers,

that was it!

Z

[TheIdeasMan]

Hi,

Always compile with a high level of warnings, at least with -Wall -Wextra -pedantic-errors. I wouldn't use -fpermissive - that's cheating :+) There is a strong risk that you are letting things go past the compiler that will only cause problems later on, and that misses the point of having warnings.

Good Luck!!

[zolo]

Thanks for the tip. The -fpermissive is there because I forgot to take it out after my long standing fight with conversion errors from char* to const cahr and so on when reading a binary file or better said trying to figure out the endianness and structure of the binary file. I took out and works like charm! :)
This was a very good shout since I would have forgotten there! thanks,

Z