Fixing Multiple Definition Linking Errors | Generated by AI
This is a multiple definition linking error — a classic C mistake when global variables are defined in a header file (variables.h) instead of just being declared there.
Let’s break down what’s happening and how to fix it.
🔍 The problem
Your error says:
multiple definition of `curl' ...
multiple definition of `nec' ...
multiple definition of `contador' ...
multiple definition of `descargadas' ...
That means your header file variables.h probably looks like this:
// variables.h (problematic)
#include <curl/curl.h>
CURL *curl;
int nec;
int contador;
int descargadas;
Every .c file that includes variables.h gets its own copy of those variables.
At link time, the linker finds multiple definitions of the same global symbols, one from each object file.
✅ The correct pattern
You must declare the globals in the header, and define them only once in a single .c file.
Step 1: Fix variables.h
Change it to:
// variables.h
#ifndef VARIABLES_H
#define VARIABLES_H
#include <curl/curl.h>
extern CURL *curl;
extern int nec;
extern int contador;
extern int descargadas;
#endif
Step 2: Define them once (e.g., in variables.c)
Create or update variables.c:
#include "variables.h"
CURL *curl = NULL;
int nec = 0;
int contador = 0;
int descargadas = 0;
Step 3: Rebuild
Clean and rebuild:
make clean
make
🧠 Why this works
externtells the compiler that the variable exists elsewhere.- Only one
.cfile actually defines it (allocates memory for it). - The linker then has one definition and multiple references → no conflict.
If you’d like, I can show you a minimal example of before/after code to make this clearer. Would you like that?