How to find the multiple definitions of a function

Question

I wrote a findDialog which finds the text searched. When I give make command,it returns

g++ -Wl,-O1 -o findDialog FindDialog.o main.o moc_FindDialog.o    -L/usr/lib -lQtGui -lQtCore -lpthread 
moc_FindDialog.o: In function `FindDialog::findClicked()':
moc_FindDialog.cpp:(.text+0x20): multiple definition of `FindDialog::findClicked()'
FindDialog.o:FindDialog.cpp:(.text+0x30): first defined here
moc_FindDialog.o: In function `FindDialog::enableFindButton(QString const&)':
moc_FindDialog.cpp:(.text+0x50): multiple definition of `FindDialog::enableFindButton(QString const&)'
FindDialog.o:FindDialog.cpp:(.text+0x0): first defined here
collect2: ld returned 1 exit status
make: *** [findDialog] Error 1

I have searched the problem for hours, but I can not understand what the problem stems from. What can cause multiple definition of error?

Solution 1

Writing function definitions in header files, and then #includeing these header files in multiple .cpps in your project. Contrary to popular misconception, header guards do not protect you from this.

Write only the following in headers:

• Class definitions
• • May include inline definitions for member functions
• Non-member variable declarations
• Non-member function declarations
• Template/inline function definitions

Put everything else in "source files".

Solution 2

Vlad Lazarenko's answer is good.

I just add another possibility that I met when using QT/C++:

When you declare a slot, you don't need to write a definition (implementation), otherwise, you will get an error: multiple definition

Comments

[stedkka]

Yes, you are right about header guards which are widely advised to use to solve the problem . However they didn't help.

[Lightness Races in Orbit]

@stedkka: Header guards solve a subtly different problem (which is, speaking very generally, multiple declaration rather than definition).