[英]Initializing a struct from a constructor
我回到寫一些C ++的過程中,老實說,我很生銹。 如果我只是知道如何正確地表達它的話,我會很快找到我的問題的答案,但是我仍然感謝您的幫助。
sanitycheck.cpp:
#include <string>
using namespace std;
typedef struct STR_1 {
int val_a, val_b;
STR_1 (int a, int b)
{ val_a = a; val_b = b; }
} STR_1;
typedef struct STR_2{
string name;
STR_1 myStr1;
STR_2 (string n, STR_1 s)
{ name=n; myStr1 = s; }
} STR_2;
int main(){
return 0;
} // end main
當我嘗試使用g++ -o sanitycheck ./test/sanitycheck.cpp
進行編譯時,得到以下信息:
./test/sanitytest.cpp: In constructor ‘STR_2::STR_2(std::string, STR_1)’:
./test/sanitytest.cpp:25:3: error: no matching function for call to ‘STR_1::STR_1()’
{ name=name; myStr1 = &s; }
^
./test/sanitytest.cpp:25:3: note: candidates are:
./test/sanitytest.cpp:11:3: note: STR_1::STR_1(int*, int*)
STR_1 (int *a, int *b)
^
./test/sanitytest.cpp:11:3: note: candidate expects 2 arguments, 0 provided
./test/sanitytest.cpp:7:16: note: STR_1::STR_1(const STR_1&)
typedef struct STR_1 {
^
./test/sanitytest.cpp:7:16: note: candidate expects 1 argument, 0 provided
./test/sanitytest.cpp:25:23: error: no match for ‘operator=’ (operand types are ‘STR_1’ and ‘STR_1*’)
{ name=name; myStr1 = &s; }
^
./test/sanitytest.cpp:25:23: note: candidate is:
./test/sanitytest.cpp:7:16: note: STR_1& STR_1::operator=(const STR_1&)
typedef struct STR_1 {
^
./test/sanitytest.cpp:7:16: note: no known conversion for argument 1 from ‘STR_1*’ to ‘const STR_1&’
我不清楚的一件事是為什么STR_1 myStr1;
為什么STR_1 myStr1;
的STR_2
需要調用STR_1
構造函數嗎? 我不能用這兩種類型初始化
int main()
{
STR_1 bob = STR_1(5,6);
STR_2 tom = STR_2('Tom',bob);
return 0;
}
謝謝!
除非從OP的注釋鏈接中不清楚,否則:
typedef struct STR_2{
string name;
STR_1 myStr1;
STR_2 (string n, STR_1 s) // here the myStr1 default constructor is called
{ name=name; myStr1 = s; }
} STR_2;
要求STR_1
是默認可構造的。 為了變通,您必須構造成員STR_1 myStr1;
在構造函數的初始化列表中:
STR_2 (string n, STR_1 s) : name(n), myStr1(s) {}
這將調用編譯器生成的STR_1
副本構造函數,而不是默認的構造函數(通過提供自定義構造函數來抑制其自動生成)。
另一種選擇是使用指向STR_1
的指針:
typedef struct STR_2{
string name;
std::unique_ptr<STR_1> myStr1;
STR_2 (string n, STR_1 s)
{ name=name; myStr1 = std::make_unique<STR_1>(s); } //just for the sake of explanation
//again, this would be better
//done in the initializer list
} STR_2;
然而,僅出於充分的理由,我才選擇第一種選擇。
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