如何检查字符串是否可以转换为一个浮动？ [英] How can I check if a string can be converted to a float?

问题描述

首先我上下文是一个编译器的作家谁需要浮点文字（字符串）转换成浮点/双精度值。所以我pretty相信这是一个愚蠢的总新手问题我没有做任何浮动点规划在过去15年。

First my context is that of a compiler writer who needs to convert floating point literals (strings) into float/double values. I haven't done any floating point programming the last 15 years so i'm pretty sure this is a total stupid newbie question.

double res; 
errno=0; 
*res = strtod((const char*)literal,NULL); 
if (errno==ERANGE) throw_a_literal_out_of_range_exception();
return res;

但在C运行时库中没有strtof功能？

but there is no "strtof" function in the c runtime library?

编辑：澄清。我已经知道该字符串'文字'是一个C浮点一个有效的模式。它已经通过一个普通的前pression测试。我只是想检查是否有一个范围/ precision问题。

To clarify. I already know that the string 'literal' is a valid pattern for a C floating point. It already passed a regular expression test. I just want to check if there is a range/precision problem.

究其原因，埃菲尔铁塔源$ C ​​$ C，用户可以写

The reason is in Eiffel source code a user can write

a := {REAL_32} 3.1415
b := {REAL_32} 3.0E200

要投的书面浮点数explit一个32位浮点。我觉得在第二种情况下，编译器应该检测值超出范围，并引发错误或至少是一个警告。

To cast a written floating point number explit to a 32bit floating point. I think in the second case the compiler should detect that the value is out of range and raise an error or at least a warning.

推荐答案

既然你已经在你的价值双击，你可以检查它是否是的范围之外浮动：

Since you have your value in a double, you can just check if it's outside of the range of float:

#include <stdlib.h>
#include <stdio.h>
#include <float.h>

int main(int argc, char *argv[])
{
    double d = FLT_MAX;
    if (argc > 1) {
        d = strtod(argv[1], NULL);
    }
    if ((d > 0 && (d > FLT_MAX || d < FLT_MIN))
                || (d < 0 && (d < -FLT_MAX || d > -FLT_MIN)))
        printf("Invalid float: %g\n", d);
    else
        printf("Valid: %g\n", d);

    return EXIT_SUCCESS;
}

运行程序：

$ ./a.out
Valid: 3.40282e+38
$ ./a.out 3.5e38
Invalid float: 3.5e+38
$ ./a.out -1e40
Invalid float: -1e+40

您可能会或可能不会需要添加一个测试为正确的关于strtod（）回归，这取决于是否有溢出的可能性双键入为好。

You may or may not need to add a test for correct strtod() return, depending upon whether there's a possibility of an overflow in double type as well.

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