从输入获得的数字最好的方法？ [英] Best way to get numbers from input?

问题描述

我想循环逐个字符从有文字和数字的输入文件。我想我可能只是环......

I would like to loop character by character from an input file that has text and numbers. I thought I could just loop...

   char count;

    while( c != ' ' && c != '\n' && c != '\t' ) {
        count += c;
        c = fgetc(fp);
    }

说从文本文件中得到11，然后使用的atoi转换为int但后来我意识到，我只是将ASCII码。我是相当新的C和从我了解的字符串只是字符数组 - 这是否意味着我必须把1和1变成一个字符数组？但后来我不得不担心数组大小和转换，要多少？

to say get "11" from the text file and then use atoi to convert to an int but I then realized I'm just adding ASCII numbers. I'm fairly new to C and from what I understand strings are just char arrays - does this mean I have to put "1" and "1" into a char array? But then I would have to worry about array size and converting that to a number?

推荐答案

虽然它看起来像自然的解决方案，我通常反对使用意见的fscanf（）上潜在的恶意输入

While it looks like the natural solution, I usually advice against using fscanf() on potentially malformed input.

有几个问题的功能，其中包括：

There are several issues with the function, among them:

• 无法从错误（短 FTELL（） / fseek的（）），因为正常恢复你不知道在哪里的究竟的它停止解析输入。


• 与它导致使用未初始化值的难易程度（如果格式未能匹配输入，而你没有正确检查返回code）。


• 某些角落情况下，的fscanf（）扼流圈输入其中，的atoi（） / 与strtol（）不（<一个href=\"http://stackoverflow.com/questions/1425730/difference-between-scanf-and-strtol-strtod-in-parsing-numbers\">\"0xz\"...).

• The inability to recover gracefully from an error (short of ftell() / fseek()), because you don't know where exactly it stopped parsing input.
• The ease with which it leads to using uninitialized values (if the format failed to match the input, and you didn't check the return code properly).
• Some corner cases where fscanf() chokes on input where atoi() / strtol() don't ("0xz"...).

这一切，遇事推诿的fscanf（）阅读的格式正确的唯一的输入，也就是你自己的程序曾在一个已知的格式之前写的东西。

All this relegates fscanf() to read well-formatted input only, i.e. things your own program had written before in a known format.

对于任何类型的输入是可能的不的是预期的格式，我建议每次读一本线（与fgets（）），并分析其内存，例如使用的 与strtol（） ：

For any kind of input that might not be in the expected format, I recommend reading a line at a time (fgets()), and parsing it in-memory, for example with strtol():

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

#define LINE_BUFFER_SIZE 256;

// ...
char line[ LINE_BUFFER_SIZE ];
fgets( line, LINE_BUFFER_SIZE, fp );
char * scanptr;
errno = 0;
long number = strtol( line, &scanptr, 0 );
if ( scanptr == line )
{
    // not a number...
}

• scanptr 现在指向到数字分析结束。


• 数量包含数字解析，0，如果行没有用号， LONG_MAX RESP开始。 LONG_MIN 如发现数量超出长范围（在这种情况下，的errno == ERANGE 以及）。


• scanptr now points to where number parsing ended.
• number contains the number parsed, 0 if line did not start with a number, and LONG_MAX resp. LONG_MIN if the number found is out of long range (in which case errno == ERANGE as well).

我不知道您的具体要求，所以我不能给，因为如果你没有找到一个号码，或做什么用文字做什么一个很好的例子。但是，因为你得到了线（或更长行的第一个 LINE_BUFFER_SIZE 字符...）在内存中，你有的字符串函数的在您的处置。 strpbrk（行，0123456789） 可以用来搜索下一个数字或 strpbrk（行，+ -0123456789）如果您可能有 + - 在输入...

I don't know your exact requirements, so I cannot give a good example for what to do if you don't find a number, or what to do with the text. But since you got the line (or, the first LINE_BUFFER_SIZE characters of a longer line...) in memory, you have the whole range of the string functions at your disposal. strpbrk( line, "0123456789" ) could be used to scan for the next digit, or strpbrk( line, "+-0123456789" ) if you might have +- in your input...

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