解析一个逗号用C使用的fscanf分隔的文件（） [英] Parsing a comma separated file using C using fscanf()
问题描述
我有一个数据是这样的一个文件 -
I have a file with data something like this -
Name, Age, Occupation
John, 14, Student
George, 14, Student
William, 23, Programmer
现在，我想读这样每个值（如姓名，年龄等）读出的字符串的数据
这是我的code片段 - 。
Now, I want to read the data such that each value (e.g. Name, Age etc.) are read as a string.
This is my code snippet -
....
if (!(ferror(input_fp) || ferror(output_fp))) {
while(fscanf(input_fp, "%30[^ ,\n\t]%30[^ ,\n\t]%30[^ ,\n\t]",
name, age_array, occupation) != EOF){
fprintf(stdout, "%-30s%-30s%-30s\n", name, age_array, occupation);
}
fclose(input_fp);
fclose(output_fp);
}
....
不过，这将进入一个无限循环给一些随机的输出。
这就是我所理解我的输入转换说明 30％[^，\\ n \\ t] - >读取字符串，它是在最多30个字符长，而且
不包括无论是空格，逗号，换行符或制表符。
而我读3这样的字符串。
我在哪里去了？
However, this goes into an infinite loop giving some random output.
This is how I understand my input conversion specifiers.
%30[^ ,\n\t] -> read a string that is at the maximum 30 characters long and that
DOES NOT include either a space, a comma, a newline or a tab character.
And I am reading 3 such strings.
Where am I going wrong?
推荐答案
OP的
fscanf(input_fp, "%30[^ ,\n\t]%30[^ ,\n\t]%30[^ ,\n\t]", ...
不消耗，还是的'\\ n'在文本文件中。随后的fscanf（）尝试也失败并返回一个0值，这不是 EOF ，会导致一个无限循环。
does not consume the ',' nor the '\n' in the text file. Subsequent fscanf() attempts also fail and return a value of 0, which not being EOF, causes an infinite loop.
虽然OP请求的fscanf（）液，与fgets（）/的sscanf（）更好地处理潜在的IO和解析错误。
Although OP requested a fscanf() solution, a fgets()/sscanf() better handles potential IO and parsing errors.
FILE *input_fp;
FILE *output_fp;
char buf[100];
while (fgets(buf, sizeof buf, input_fp) != NULL) {
char name[30]; // Insure this size is 1 more than the width in scanf format.
char age_array[30];
char occupation[30];
#define VFMT " %29[^ ,\n\t]"
int n; // Use to check for trailing junk
if (3 == sscanf(buf, VFMT "," VFMT "," VFMT " %n", name, age_array,
occupation, &n) && buf[n] == '\0') {
// Suspect OP really wants this width to be 1 more
if (fprintf(output_fp, "%-30s%-30s%-30s\n", name, age_array, occupation) < 0)
break;
} else
break; // format error
}
fclose(input_fp);
fclose(output_fp);
而不是调用 FERROR（），检查的返回值与fgets（）， fprintf中（）。
可疑OP未申报的场缓冲器均 [30] 和调整 scanf（）的相应。
Suspect OP's undeclared field buffers were [30] and adjusted scanf() accordingly.
关于详细信息，如果（3 ==的sscanf（BUF，VFMT，...
的如果（3 ==的sscanf（...）及和放大器; BUF [N] =='\\ 0'）{为真时：
1）正是3 ％29 [^ \\ n \\ t]格式说明至少在1每个scanf函数字符每个。结果
2） BUF [N] 是字符串的结尾。 N 通过％N说明设置。在preceding 在％N最后<$ C后会引起任何下列空白$ C>％29 [^ \\ n \\ t]被消耗。 scanf（）的看到％N，它引导它来设置电流从扫描开始偏移是分配给 INT 按＆放指了指; N
The if (3 == sscanf(...) && buf[n] == '\0') { becomes true when:
1) exactly the 3 "%29[^ ,\n\t]" format specifiers each scanf in at least 1 char each.
2) buf[n] is the end of the string. n is set via the "%n" specifier. The preceding ' ' in " %n" causes any following white-space after the last "%29[^ ,\n\t]" to be consumed. scanf() sees "%n", which directs it to set the current offset from the beginning of scanning to be assign to the int pointed to by &n.
VFMT，VFMT，VFMT％N是由编译器连接起来结果％29 [^ \\ n \\ t]，％29 [^ \\ n \\ t]，％29 [^ \\ n \\ T]％N。结果
我觉得前者更容易比后者维护。
"VFMT "," VFMT "," VFMT " %n" is concatenated by the compiler to
" %29[^ ,\n\t], %29[^ ,\n\t], %29[^ ,\n\t] %n".
I find the former easier to maintain than the latter.
在％29 [^ \\ n \\ t]指引的sscanf（）来的首次太空扫描结束（消费，而不是保存）0个或更多的空格（，'\\ T'，的'\\ n'等）。其余的指导的sscanf（）消耗，节省的任何的1至29 字符 除了的，，的'\\ n'，'\\ t ，然后附加一个'\\ 0'。
The first space in " %29[^ ,\n\t]" directs sscanf() to scan over (consume and not save) 0 or more white-spaces (' ', '\t', '\n', etc.). The rest directs sscanf() to consume and save any 1 to 29 char except ',', '\n', '\t', then append a '\0'.
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