C++類的靜態成員初始化

Question

我有以下代碼：

class employee { 
public: 
    static int last_id; 
    ... 

}; 

int main() { 
    employee::last_id=0; 
} 

當我嘗試運行它，它提供了以下錯誤：

Undefined symbols for architecture x86_64: 
    "employee::last_id", referenced from: 
     _main in chap7-F3IpS1.o 
ld: symbol(s) not found for architecture x86_64 
clang: error: linker command failed with exit code 1 (use -v to see invocation) 
[Finished in 0.3s with exit code 1] 

Answer 1

int employee::last_id=0; 
int main() { 
    [...] 

} 

Answer 2

你只是聲明瞭靜態數據成員但沒有定義它。在全局命名空間的主要之前寫入

int employee ::last_id; 

儘管您明確指定了初始化程序，但它將被初始化爲0。