将字符串转换为整数类型T，检查是否存在溢出

您的解决方案看起来不错。然而，如果您想要更好的编译时优化，您应该考虑进行模板专业化。在给出的代码中，您根据类型进行分支。然而，这可能会被编译到代码中，而不是在编译时解决(在已经可能的情况下(。此外，如果您想根据类型添加额外的检查，函数很快就会变得混乱。

我写了我自己版本的转换代码，除了你的代码外，它还检查是否为整数类型提供了科学符号：

#include <type_traits>
#include <utility>
#include <string>
#include <limits>
#include <algorithm>
template <typename T>
auto to_T(const std::string &s) -> std::enable_if_t<std::is_floating_point<T>::value, std::pair<bool, T>>
{
return std::pair<bool, T>{true, T(std::stold(s))}; //read the string into the biggest floating point possible, and do a narrowing conversion
}
template <typename T>
auto to_T(const std::string &s) -> std::enable_if_t<!std::is_floating_point<T>::value && std::is_signed<T>::value, std::pair<bool, T>>
{
return ((long long)(std::numeric_limits<T>::min()) <= std::stoll(s) && //does the integer in the string fit into the types data range?
std::stoll(s) <= (long long)(std::numeric_limits<T>::max()))
? std::pair<bool, T>{true, T(std::stoll(s))}
: std::pair<bool, T>{false, 0}; //if yes, read the string into the biggest possible integer, and do a narrowing conversion
}
template <typename T>
auto to_T(const std::string &s) -> std::enable_if_t<!std::is_floating_point<T>::value && std::is_unsigned<T>::value, std::pair<bool, T>>
{
return ((unsigned long long)(std::numeric_limits<T>::min()) <= std::stoull(s) && //does the integer in the string fit into the types data range?
std::stoull(s) <= (unsigned long long)(std::numeric_limits<T>::max()))
? std::pair<bool, T>{true, T(std::stoull(s))}
: std::pair<bool, T>{false, 0}; //if yes, read the string into the biggest possible integer, and do a narrowing conversion
}
template <typename T>
auto decode(const std::string &s) -> std::enable_if_t<std::is_floating_point<T>::value, std::pair<bool, T>>
{
return s.empty() ? //is the string empty?
std::pair<bool, T>{false, 0}
: to_T<T>(s); //if not, convert the string to a floating point number
}
template <typename T>
auto decode(const std::string &s) -> std::enable_if_t<!std::is_floating_point<T>::value && std::is_signed<T>::value, std::pair<bool, T>>
{
return (s.empty() ||                                                 //is the string empty?
std::find(std::begin(s), std::end(s), '.') != std::end(s) || //or does it not fit the integer format?
std::find(std::begin(s), std::end(s), ',') != std::end(s) ||
std::find(std::begin(s), std::end(s), 'e') != std::end(s) ||
std::find(std::begin(s), std::end(s), 'E') != std::end(s))
? std::pair<bool, T>{false, 0}
: to_T<T>(s); //if not, convert the string to a signed integer value
}
template <typename T>
auto decode(const std::string &s) -> std::enable_if_t<!std::is_floating_point<T>::value && std::is_unsigned<T>::value, std::pair<bool, T>>
{
return (s.empty() ||                                                 //is the string empty?
std::find(std::begin(s), std::end(s), '.') != std::end(s) || //or does it not fit the integer format?
std::find(std::begin(s), std::end(s), ',') != std::end(s) ||
std::find(std::begin(s), std::end(s), 'e') != std::end(s) ||
std::find(std::begin(s), std::end(s), 'E') != std::end(s) ||
std::find(std::begin(s), std::end(s), '-') != std::end(s))
? //or does it have a sign?
std::pair<bool, T>{false, 0}
: to_T<T>(s); //if not, convert the string to an unsigned integer value
}

这仍然需要在平台之间进行某种程度的移植，因为std::stold、std::stoll或std::stoull可能不可用。但除此之外，它应该独立于平台类型的实现。

编辑：

我忘记了decode不应该读取数字，而是返回0的情况。现在已修复。

以下是使用istringstream并解决其注意事项的直接方法：

template<typename T>
std::pair<bool, T> decode(std::string s)
{
typedef std::pair<bool, T> Result;
if (s.empty())
return Result(false, 0);
if (!std::numeric_limits<T>::is_signed && s[0] == '-')
return Result(false, 0);
if (sizeof(T) == 1)
{
// Special case for char
std::pair<bool, short> result = decode<short>(s);
if (!result.first)
return Result(false, 0);
if (!inrange(result.second, std::numeric_limits<T>::min(), std::numeric_limits<T>::max()))
return Result(false, 0);
return Result(true, (T)result.second);
}
else
{
T value;
std::istringstream iss(s);
iss >> std::dec >> value;
return Result(!iss.fail(), value);
}
}