Question

I am trying to compile simple program under linux. These are the set of operations I performed.

[mypc@localhost programs]$ vim heap.cpp
[mypc@localhost programs]$ g++ -c heap.cpp 
[mypc@localhost programs]$ chmod 777 heap.*
[mypc@localhost programs]$ g++ -c heap.cpp 
[mypc@localhost programs]$ ./heap.o
bash: ./heap.o: Permission denied
[mypc@localhost programs]$ ls
heap.cpp  heap.o
[mypc@localhost programs]$ ls -l
total 8
-rwxrwxrwx. 1 mypc mypc   67 2009-12-28 12:01 heap.cpp
-rw-rw-r--. 1 mypc mypc 1548 2009-12-28 12:02 heap.o
[mypc@localhost programs]$ chmod 777 heap.o
[mypc@localhost programs]$ ./heap.o
bash: ./heap.o: cannot execute binary file
[mypc@localhost programs]$ 

What kind of error is this ?

Here is a program

#include<iostream>

using namespace std;
int main(){

        return 0;
}

Answer 1

The -c option tells the compiler to generate an object file, not the final binary. You still need to link your code.

If you only have a single file, you can do a compile and link in one step:

g++ heap.cpp -o heap

As you get to bigger programs, you will want to separate compilation from linking. Let’s say you want to split your code between heap.cpp and main.cpp. First you would do a compilation step and later you would link them together:

g++ -c heap.cpp
g++ -c main.cpp
g++ -o program_name heap.o main.o

Finally, by default, the linking step creates a file named a.out. If you want so specify the name, make sure to use the -o option (which isn’t necessary when compiling as the default is to convert NAME.EXTENSION to NAME.o).