I have this following simple program I am trying to compile in linux ubuntu.
Main.c
:
#include <stdio.h>
#include "Person.h"
int main()
{
struct Person1 p1 = Person1_Constructor(10, 1000);
}
Person.c
:
#include <stdio.h>
#include "Person.h"
struct Person1 Person1_Constructor(const int age, const int salary)
{
struct Person1 p;
p.age = age;
p.salary = salary;
return p;
};
Person.h
:
struct Person1
{
int age, salary;
};
struct Person1 Person1_Constructor(const int age, const int salary);
Why do I get the following error ?
/tmp/ccCGDJ1k.o: In function `main':
Main.c:(.text+0x2a): undefined reference to `Person1_Constructor'
collect2: error: ld returned 1 exit status
I am using gcc Main.c -o Main
to compile.
When we compile these files separately, the first file gives “undefined reference” for the print function, while the second file gives “undefined reference” for the main function. The way to resolve this error is to compile both the files simultaneously (For example, by using g++).
This error is often generated because you have typed the name of a function or variable incorrectly. For example, the following code: #include <stdio.h> void print_hello() { printf ("Hello!\n"); } /* To shorten example, not using argp */ int main() { Print_hello(); return 0; }
Compilation error refers to a state when a compiler fails to compile a piece of computer program source code, either due to errors in the code, or, more unusually, due to errors in the compiler itself.
The error means that the compiler try to find WinMain() but it didn't. Either you didn't declare int main() Or your project type is something other than Console. ( Normally Win32GUI)
When you link the program you need to give both Main.o and Person.o as inputs.
Build usually is done in two steps (1) compilation and (2) linking. To compile your sources do:
$ gcc -c -o Main.o Main.c
$ gcc -c -o Person.o Person.c
Or in one line:
$ gcc -c Main.c Person.c
Then the resulting object files must be linked into a single executable:
$ gcc -o Main Main.o Person.o
For small projects, of a few compilation units like yours, both step can be done in one gcc
invocation:
$ gcc -o Main Main.c Person.c
both files must be given because some symbols in Person.c
are used by Main.c
.
For bigger projects, the two step process allows to compile only what changed during the generation of the executable. Usually this is done through a Makefile.
The problem is probably occurring because you're compiling only Main.c
when you need to be compiling Main.c
and Person.c
at the same time. Try compiling it as gcc Main.c Person.c -o MyProgram
.
Whenever you have multiple files, they all need to be specified when compiling in order to resolve external references, as is the case here. The compiler will spit out object files that will later be linked into an executable. Check out this tutorial on makefiles: Make File Tutorial It helps to automate this process.
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