后来检查了这些警告：当发生时，它看起来像gcc在串联中接受两个构造是完全不同的构造（IT解释if（int（a）） = 1） as 声明阴影int变量名为a，初始化为1，该>到期之后/ 链条，它仅在使用-wall进行编译时才警告，即使到那时，它也只会抱怨，因为它认为它应该是，如果（int a = 1）将其制作名称无外括号的阴影变量，ugh。光明的一面是，将分配固定在比较中会揭示另一个问题。这是始终在警告中始终编译的一个很好的理由（-wextra有时过于健谈，但是-wall几乎总是指出真正的问题），可悲的是，这是一个相当间接的在这种情况下警告。
const int aint = std::stoi(a);
if (aint == 1) // Using ==, not =
{
bin = 60457811425;
}
else if (aint == 2) // Testing int == int, not string == int
{
bin = 60457811474;
}
else if (aint == 3) // Testing int == int, not string == int
{
bin = 6045781165;
}
或对于更简洁的代码（也没有额外的命名变量）：
switch(std::stoi(a)) {
case 1: bin = 60457811425; break;
case 2: bin = 60457811474; break;
case 3: bin = 6045781165; break;
/* Maybe put a default case here to handle invalid input? */
}
You only converted to a to an int once, you didn't do it with a legal converter ("constructing" an int from a std::string doesn't work like that, and I'd be surprised if your compiler didn't warn you), and you assigned to the result (=) rather than comparing (==) (also something I'd expect a compiler to warn you about).
Later checked about those warnings: As it happens, it looks like gcc accepts both constructs in tandem as a completely different construct (it interprets if (int(a) = 1) as declaring a shadowing int variable named a, initialized to 1, that expires after the if/else if chain; that's fun). It only warns at all if you compile with -Wall, and even then, it only complains because it thinks it should be if (int a = 1) to make the name shadowing variable without extraneous parentheses, ugh. Bright side is that fixing the assignment to a comparison would then reveal the other problem. That's a good reason to always compile with warnings turned up (-Wextra is sometimes overly chatty, but -Wall is almost always pointing out real problems), sadly it's a rather indirect warning in this case.
const int aint = std::stoi(a);
if (aint == 1) // Using ==, not =
{
bin = 60457811425;
}
else if (aint == 2) // Testing int == int, not string == int
{
bin = 60457811474;
}
else if (aint == 3) // Testing int == int, not string == int
{
bin = 6045781165;
}
Or for slightly more succinct code (and no extra named variables):
switch(std::stoi(a)) {
case 1: bin = 60457811425; break;
case 2: bin = 60457811474; break;
case 3: bin = 6045781165; break;
/* Maybe put a default case here to handle invalid input? */
}
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评论（1）
您只将
a转换为int，您就不会使用法律转换器（从<代码> std :: string 无法正常工作，如果您的编译器不警告您，我会感到惊讶），然后将分配给结果（> =），而不是比较 （==）（也希望编译器警告您）。后来检查了这些警告：当发生时，它看起来像
gcc在串联中接受两个构造是完全不同的构造（IT解释if（int（a）） = 1）as 声明阴影int变量名为a，初始化为1，该>到期之后/链条，它仅在使用-wall进行编译时才警告，即使到那时，它也只会抱怨，因为它认为它应该是，如果（int a = 1）将其制作名称无外括号的阴影变量，ugh。光明的一面是，将分配固定在比较中会揭示另一个问题。这是始终在警告中始终编译的一个很好的理由（-wextra有时过于健谈，但是-wall几乎总是指出真正的问题），可悲的是，这是一个相当间接的在这种情况下警告。先前转换一次带有有效的
stringto <<代码> int 转换器如std :: stoi，然后测试转换的int值ints，而不是std :: String反对int，例如：或对于更简洁的代码（也没有额外的命名变量）：
You only converted to
ato anintonce, you didn't do it with a legal converter ("constructing" anintfrom astd::stringdoesn't work like that, and I'd be surprised if your compiler didn't warn you), and you assigned to the result (=) rather than comparing (==) (also something I'd expect a compiler to warn you about).Later checked about those warnings: As it happens, it looks like
gccaccepts both constructs in tandem as a completely different construct (it interpretsif (int(a) = 1)as declaring a shadowingintvariable nameda, initialized to1, that expires after theif/else ifchain; that's fun). It only warns at all if you compile with-Wall, and even then, it only complains because it thinks it should beif (int a = 1)to make the name shadowing variable without extraneous parentheses, ugh. Bright side is that fixing the assignment to a comparison would then reveal the other problem. That's a good reason to always compile with warnings turned up (-Wextrais sometimes overly chatty, but-Wallis almost always pointing out real problems), sadly it's a rather indirect warning in this case.Convert it once up front with a valid
stringtointconverter likestd::stoi, and then test the convertedintvalue against otherints, notstd::stringagainstint, e.g.:Or for slightly more succinct code (and no extra named variables):