使用 istreamstream 模拟 sscanf's %*s

发布于 2024-12-12 06:15:18 字数 438 浏览 0 评论 0原文

可能的重复：
sscanf() 的 C++ 替代方案

我有以下代码

sscanf(s, "%*s%d", &d);

行我如何使用 <代码> istringstream ？

我尝试了这个：

istringstream stream(s);
(stream >> d);

但由于 sscanf() 中的 *s ，它不正确。

原文

Possible Duplicate:
C++ alternative to sscanf()

I have the following line of code

sscanf(s, "%*s%d", &d);

How would I do this using istringstream?

I tried this:

istringstream stream(s);
(stream >> d);

But it is not correct because of *s in sscanf().

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慵挽 2024-12-19 06:15:18

与 sscanf 一起使用的 %*s 基本上意味着忽略一个字符串（直到空格的任何字符），然后您就可以告诉它读取一个整数（%*s%d）。在这种情况下，星号 (*) 与指针无关。

因此，使用 stringstream，只需模拟相同的行为即可；读入一个字符串，在读入整数之前可以忽略该字符串。

int d;
string dummy;
istringstream stream(s);

stream >> dummy >> d;

IE。使用以下小程序：

#include <iostream>
#include <sstream>
using namespace std;

int main(void)
{
   string s = "abc 123";

   int d;
   string dummy;
   istringstream stream(s);

   stream >> dummy >> d;

   cout << "The value of d is: " << d << ", and we ignored: " << dummy << endl;

   return 0;
}

输出将是：d 的值为：123，我们忽略了：abc。

The %*s used with sscanf basically means to ignore a string (any characters up until a whitespace), and then after that you're telling it to read in an integer (%*s%d). The asterisk (*) has nothing to do with pointers in this case.

So using stringstreams, just emulate the same behaviour; read in a string that you can ignore before you read in the integer.

int d;
string dummy;
istringstream stream(s);

stream >> dummy >> d;

ie. With the following small program:

#include <iostream>
#include <sstream>
using namespace std;

int main(void)
{
   string s = "abc 123";

   int d;
   string dummy;
   istringstream stream(s);

   stream >> dummy >> d;

   cout << "The value of d is: " << d << ", and we ignored: " << dummy << endl;

   return 0;
}

the output will be: The value of d is: 123, and we ignored: abc.

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柏林苍穹下 2024-12-19 06:15:18

您的代码中没有指针操作。

正如 AusCBloke 所说，您需要先读取所有不需要的字符将 int 转换为 std::string。您还希望确保处理 s 的格式错误的值，例如具有任何整数的值。

#include <cassert>
#include <cstdio>
#include <sstream>

int main()
{
    char s[] = "Answer: 42. Some other stuff.";
    int d = 0;

    sscanf(s, "%*s%d", &d);
    assert(42 == d);

    d = 0;

    std::istringstream iss(s);
    std::string dummy;
    if (iss >> dummy >> d)
    {
        assert(dummy == "Answer:");
        assert(42 == d);
    }
    else
    {
        assert(!"An error occurred and will be handled here");
    }
}

There is no pointer manipulation in your code.

As AusCBloke has said, you need to read the all of the unwanted characters before the int into a std::string. You also want to ensure that you handle malformed values of s, such as those with any integers.

#include <cassert>
#include <cstdio>
#include <sstream>

int main()
{
    char s[] = "Answer: 42. Some other stuff.";
    int d = 0;

    sscanf(s, "%*s%d", &d);
    assert(42 == d);

    d = 0;

    std::istringstream iss(s);
    std::string dummy;
    if (iss >> dummy >> d)
    {
        assert(dummy == "Answer:");
        assert(42 == d);
    }
    else
    {
        assert(!"An error occurred and will be handled here");
    }
}

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