Red Hat Bugzilla – Bug 247167
"undefined reference" error from g++ for private class variables.
Last modified: 2007-11-30 17:12:09 EST
Description of problem: g++ and/or ld report "undefined reference" error when processing private class variables (i.e., static variables in the private part of a class). Version-Release number of selected component (if applicable): Package is gcc-4.1.2-13.fc6.src.rpm, g++ reports version as "g++ (GCC) 4.1.2 20070626 (Red Hat 4.1.2-13)". How reproducible: Can be reproduced with the following program, t.cpp: #include <iostream> class A { public: void setStr(char * strIn) { privStr = strIn; } void dump() { std::cout << "privStr = \"" << privStr << "\"\n"; } private: static char * privStr; }; int main(int argc, char ** argv) { A * a = new A(); a->setStr("new value"); a->dump(); } Steps to Reproduce: 1. g++ t.cpp -o t 2. 3. Actual results: /tmp/ccRpYHoY.o: In function `A::setStr(char*)': t.cpp:(.text._ZN1A6setStrEPc[A::setStr(char*)]+0x13): undefined reference to `A::privStr' /tmp/ccRpYHoY.o: In function `A::dump()': t.cpp:(.text._ZN1A4dumpEv[A::dump()]+0x10): undefined reference to `A::privStr' collect2: ld returned 1 exit status Expected results: Successful compilation and creation of an executable file. Additional info: This problem also occurs with the latest g++ supplied by and running on gentoo on an athlon.
Please study ISO C++98, [class.static.data]/2: "The declaration of a static data member in its class definition is not a definition and may be of an incomplete type other than cv-qualified void. The definition for a static data member shall appear in a namespace scope enclosing the member's class definition. In the definition at namespace scope, the name of the static data member shall be qualified by its class name using the :: operator. The initializer expression in the definition of a static data member is in the scope of its class (3.3.6). [Example: class process { static process* run_chain; static process* running; }; process* process::running = get_main(); process* process::run_chain = running; The static data member run_chain of class process is defined in global scope; the notation process::run_chain specifies that the member run_chain is a member of class process and in the scope of class process. In the static data member definition, the initializer expression refers to the static data member running of class process. ] " In particular, you get the undefined reference because you forgot to define the static data member variable.
You a correct, of course. My apologies.