C语言 从标准输入 (C) 读取未知数量的整数
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原文地址: http://stackoverflow.com/questions/2195823/
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reading unknown number of integers from stdin (C)
提问by huhuhuuu
I need to read an input file like :
我需要读取一个输入文件，如：
1
19 20 41 23
2
41 52 43
3
90 91 941
4
512
5
6
51 61
Each odd line is an integer. Each even line is unknown number of integers.
每个奇数行是一个整数。每个偶数行都是未知数量的整数。
It is very easy in C++
在 C++ 中很容易
while( cin >> k ){
............
}
I'm not so used to C, so I couldnt make it in C. Any ways to do it?
我不太习惯 C，所以我不能用 C。有什么方法可以做到吗？
回答by Sean Bright
Running your input file through:
通过以下方式运行您的输入文件：
#include <stdio.h>
int main() {
int k;
while (scanf("%d", &k) == 1) {
printf("read number: %d\n", k);
}
return 0;
}
Results in:
结果是：
read number: 1 read number: 19 read number: 20 read number: 41 read number: 23 read number: 2 read number: 41 read number: 52 read number: 43 read number: 3 read number: 90 read number: 91 read number: 941 read number: 4 read number: 512 read number: 5 read number: 6 read number: 51 read number: 61
This is the C analog of the code you reference in your original question.
这是您在原始问题中引用的代码的 C 模拟。
回答by Dietrich Epp
The way I would do it is to break it down into two operations: read a line, then read the integers in that line. Here is a lazy implementation using the standard C library:
我的做法是将其分解为两个操作：读取一行，然后读取该行中的整数。这是使用标准 C 库的惰性实现：
char line[1024], *p, *e;
long v;
while (fgets(line, sizeof(line), stdin)) {
p = line;
for (p = line; ; p = e) {
v = strtol(p, &e, 10);
if (p == e)
break;
// process v here
}
}
回答by Alok Singhal
I would break the program in different tasks.
我会在不同的任务中破坏程序。
The first step is to be able to read a pair of lines, the first line which tells you the number of numbers to read, and then the second line to read the actual numbers. For this, a function called something like read_setmight be useful. It should be able to return the numbers read, and signal end of file as well as errors. For this, we can define a data structure such as:
第一步是能够读取一对行，第一行告诉您要读取的数字数量，然后第二行读取实际数字。为此，一个名为 like 的函数read_set可能会很有用。它应该能够返回读取的数字，并发出文件结束和错误的信号。为此，我们可以定义一个数据结构，例如：
struct numbers {
long *data; /* or choose a type depending upon your needs */
size_t len;
};
and then we can declare our function with the prototype:
然后我们可以用原型声明我们的函数：
int read_set(FILE *fp, struct numbers *num);
The function will allocate memory for num->data, and set num->lento the correct value. It returns 0 for success, and a set of error conditions otherwise. We might get fancy and use an enumfor return statuses later. For now, let's say that 0 = success, 1 = end of file, and everything else is an error.
该函数将为 分配内存num->data，并设置num->len为正确的值。它返回 0 表示成功，否则返回一组错误条件。稍后我们可能会喜欢并使用enumfor 返回状态。现在，假设 0 = 成功，1 = 文件结束，其他一切都是错误。
The caller then calls read_set()in a loop:
然后调用者read_set()循环调用：
struct numbers numbers;
int status;
while ((status = read_set(fp, &numbers)) == 0) {
/* process numbers->data, and then free it */
}
if (status == 1) {
/* hit end of file, everything is OK */
} else {
/* handle error */
}
For implementing read_set(): it has to read two lines. There are many implementations of reading a full line in C, so you can use any of them, and read a line first, then sscanf()/strtoul()it for one number (check its return value!). Once you have the number of numbers, n, you can read the next line in memory, and do:
为了实现read_set()：它必须读取两行。在 C 中有许多读取整行的实现，因此您可以使用它们中的任何一个，然后先读取一行，然后sscanf()/strtoul()它为一个数字（检查其返回值！）。一旦你有了数字的数量，n就可以读取内存中的下一行，然后执行：
num->data = malloc(n * sizeof *num->data);
num->len = n;
You can then repeatedly call sscanf()or strtol()to store numbers in num->data. You should put in checks to make sure exactly nnumbers are on that line.
然后，您可以重复呼叫sscanf()或strtol()将号码存储在 中num->data。您应该进行检查以确保n该行上的数字准确无误。
Note that you can write read_set()in other ways too: read a line character by character, and parse the numbers as you read them. This has the advantage of going over the data only once, and not needing a big buffer to store the whole input line in memory, but the disadvantage is doing low-level stuff yourself and reading data character-by-character may be slow.
请注意，您也可以用read_set()其他方式书写：逐个字符读取一行，并在读取数字时解析它们。这样做的好处是只遍历一次数据，不需要大缓冲区来将整个输入行存储在内存中，但缺点是自己做低级的事情，逐个字符读取数据可能很慢。
回答by Mubdiur Rahman Rafi
I came up with a solution like this:
我想出了一个这样的解决方案：
while(scanf("%d%c", &n, &ch)!=EOF)
{
if(ch=='\n') break;
/* rest of your code */
}
回答by Jason Williams
I would do one of:
我会做以下之一：
fgetc() to read individual characters and parse them yourself (accumulate digits until you hit whitespace and you have an integer to convert with atoi(); if the whitespace is a newline, then it terminates a list of integers)
fgets() to read a line at a time, and then parse the string (again, look for whitespace separating the values) that it returns.
fgetc() 读取单个字符并自己解析它们（累积数字，直到遇到空格并且您有一个整数可以用 atoi() 进行转换；如果空格是换行符，则它终止一个整数列表）
fgets() 一次读取一行，然后解析它返回的字符串（再次查找分隔值的空格）。
回答by Cogsy
have a look at getc(3) or scanf(3)
看看 getc(3) 或 scanf(3)
