OK. I finally found a solution and it seems to work.
I just needed to wrap it with this:
extern āCā {
}

I hope this is THE way to do it right.

Vincent

Here for anyone that may is running into the same problem:

easyLase.h

extern "C" {
int easyLaseGetCardNum();
int easyLaseWriteFrameUncompressed(int cardNumber, unsigned char *dataBuffer, unsigned int dataCounter, unsigned int speed);
int easyLaseWriteFrame(int cardNumber, unsigned char *dataBuffer, unsigned int dataCounter, unsigned int speed);
int easyLaseWriteFrameNR(int cardNumber, unsigned char *dataBuffer, unsigned int dataCounter, unsigned int speed, unsigned int repeat);
int easyLaseStop(int cardNumber);
int easyLaseWriteDMX(int cardNumber, unsigned char * dmxBuffer);
int easyLaseDMXOut(int cardNumber, unsigned char * dmxBuffer, unsigned int baseAddress, unsigned int channelCount);
int easyLaseGetDMX(int cardNumber, unsigned char * dmxBuffer);
int easyLaseDMXIn(int cardNumber, unsigned char * dmxBuffer, unsigned int baseAddress, unsigned int channelCount);
int easyLaseWriteTTL(int cardNumber, unsigned int ttl);
int easyLaseGetLastError(int cardNumber);
int easyLaseGetStatus(int cardNumber);
int easyLaseClose();
typedef struct {
unsigned short x; // 2 Bytes Value 0 - 4095 X-Coordinate
unsigned short y; // 2 Bytes Value 0 - 4095 Y-coordinate
unsigned char r; // 1 Byte Value 0 - 255 Red
unsigned char g; // 1 Byte Value 0 - 255 Green
unsigned char b; // 1 Byte Value 0 - 255 Blue
unsigned char i; // 1 Byte Value 0 - 255 Intensity
} __attribute__((packed)) EasyLaseData, *EasyLasePoint;
}