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[英]no match for 'operator*' (operand type is 'const string' {aka 'const std::__cxx11::basic_string<char>'})
[英]error: no match for 'operator+=' (operand types are 'long double' and 'std::__cxx11::basic_string<char>')
我需要從可以是任何數據類型的元組中讀取值,然后如果它們是數字就添加它們,或者如果它們可轉換為字符串則將它們連接起來。
tuple<int32_t, bool, string, float, const char*, char, int> t{10, true, "Modern", 2.3f, "C++", 'e', 13}; // Example Tuple
因此,我認為模板將是可行的方法,但即使添加數字和 const char* 的情況也不可能發生,但我收到了編譯錯誤。
no match for 'operator+=' (operand types are 'long double' and 'std::__cxx11::basic_string<char>')
22 | numericSum += tupleValue;
| ~~~~~~~~~~~^~~~~~~~~~~~~
error: in evaluation of 'operator+=(long double, const char*)'
那么有什么方法可以修改我的代碼來解決這個問題呢? 是否有一種類似於 is_arithmetic 的簡單方法來檢測字符和字符串?
// Based on the datatype of the tupleValue, we either add, concatenate or ignore the value
template<typename T>
void interact_with_tuple(T tupleValue, long double &numericSum, string &stringConcatenation, int &argumentsIgnored){
// Check for chars
if (is_convertible<T*, string>::value){
stringConcatenation += tupleValue;
}
// Check for strings and char pointers
else if (is_convertible<T, string>::value){
stringConcatenation += tupleValue;
}
// Check for integers and floating point numbers but exclude bools
else if (is_arithmetic<T>::value && !is_same<T, bool>::value){
numericSum += tupleValue;
}
else{
argumentsIgnored += 1;
}
cout << tupleValue << endl;
}
主函數中的代碼:
int main(){
tuple<int32_t, bool, string, float, int> t{10, true, "Modern", 2.3f, 13}; // Example Tuple
long double NumericSum = 0.0;
string stringConcatenation = "";
int argumentsIgnored = 0; // Im going to assume I don't need a long long for this
// Iterate through Tuple
apply([&](auto&&... args){((interact_with_tuple(args, NumericSum, stringConcatenation, argumentsIgnored)), ...);}, t);
cout << "NumericSum: " << NumericSum << endl;
cout << "stringConcatenation: " << stringConcatenation << endl;
cout << "argumentsIgnored: " << argumentsIgnored << endl;
}
您可以使用 C++17' is new compile-time conditional if constexpr
。 它只會編譯您需要的塊並丟棄其余的塊。
if constexpr (std::is_convertible<T*, std::string>::value){
stringConcatenation += tupleValue;
}
// Check for strings and char pointers
else if constexpr (std::is_convertible<T, std::string>::value){
stringConcatenation += tupleValue;
}
// Check for integers and floating point numbers but exclude bools
else if constexpr (std::is_arithmetic<T>::value && !std::is_same<T, bool>::value){
numericSum += tupleValue;
}
else{
argumentsIgnored += 1;
}
現場演示: https : //godbolt.org/z/rff88hM8r
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