Parsing a line in C - c

I have a file, in which each line contains several words that are separated by variable amount of whitespace characters (spaces and tabs). For example:
do that param1 param2 param3
do this param1
(The number of words in a line is unknown in advance and is unbounded)
I'm looking for a way to parse such a line in plain C, so that I'll have a pointer to string containing the first word, a pointer to a string containing the second word, and a pointer to a string containing everything else (that is - all of the line, except the first two words). The idea is that the "rest of the line" string will be further parsed by a callback function, determined by the first two words).
Getting the first two words is easy enough (a simple sscanf), but I have no idea how to get the "rest of the line" pointer (As sscanf stops at whitespace, and I don't know the amount of whitespace before the first word, and between the first and the second word).
Any idea will be greatly appreciated.

You can use sscanf for the rest of the line as well. You just use a "scanset" conversion instead of a string conversion:
char word1[256], word2[256], remainder[1024];
sscanf(input_line, "%255s %255s %1023[^\n]", word1, word2, remainder);

Related

Meaning of [^:]: format string in scanf

I found this in some code and could not understand what it does:
scanf("%[^:]:%[^:]:%[^:\n]", a, b, c);
There was no mention of the [^:]: format string in the C documentation and I am quite confused.
The format string %[..] is for specifying the possible characters. For example %[A-DF] is for A, B, C, D, and F. And the ^ at the beginning is for any character excluding the characters specified. Hence, the first format string is for reading characters excluding colon. And the next is colon, and so on. You may test the scanf for the following input:
Adam:And:Apple
Important thing you should remember is, scanf() function accepts the arguments how it is specified.
For example:
scanf("%d %d",&a,&b);
assuming a and b are integer.
In the command line you have to input a and then followed by space and then b.because you have given a space in-between two "%d's". if you are giving n number of spaces are other character then you have to enter in-between those character before the value gets accepted.
Hence in your case:
you enter the string not containing ":" in it.
Consider this case, if you want to enter a string containing ":" in it.
For example:
"some:init" is the string then, in first %[^:] the string "some" is stored,then comes the ":" and then in second %[^:] it stores init. Then it wait for one more ":" and then the string not containing ":".
ultimately accepting the input in this format doesn't fetch any thing.
The only thing matters is how you print it on to the console.

Sscanf not returning what I want

I have the following problem:
sscanf is not returning the way I want it to.
This is the sscanf:
sscanf(naru,
"%s[^;]%s[^;]%s[^;]%s[^;]%f[^';']%f[^';']%[^;]%[^;]%[^;]%[^;]"
"%[^;]%[^;]%[^;]%[^;]%[^;]%[^;]%[^;]%[^;]%[^;]%[^;]%[^;]%[^;]"
"%[^;]%[^;]%[^;]%[^;]%[^;]%[^;]",
&jokeri, &paiva1, &keskilampo1, &minlampo1, &maxlampo1,
&paiva2, &keskilampo2, &minlampo2, &maxlampo2, &paiva3,
&keskilampo3, &minlampo3, &maxlampo3, &paiva4, &keskilampo4,
&minlampo4, &maxlampo4, &paiva5, &keskilampo5, &minlampo5,
&maxlampo5, &paiva6, &keskilampo6, &minlampo6, &maxlampo6,
&paiva7, &keskilampo7, &minlampo7, &maxlampo7);
The string it's scanning:
const char *str = "city;"
"2014-04-14;7.61;4.76;7.61;"
"2014-04-15;5.7;5.26;6.63;"
"2014-04-16;4.84;2.49;5.26;"
"2014-04-17;2.13;1.22;3.45;"
"2014-04-18;3;2.15;3.01;"
"2014-04-19;7.28;3.82;7.28;"
"2014-04-20;10.62;5.5;10.62;";
All of the variables are stored as char paiva1[22] etc; however, the sscanf isn't storing anything except the city correctly. I've been trying to stop each variable at ;.
Any help how to get it to store the dates etc correctly would be appreciated.
Or if there's a smarter way to do this, I'm open to suggestions.
There are multiple problems, but BLUEPIXY hit the first one — the scan-set notation doesn't follow %s.
Your first line of the format is:
"%s[^;]%s[^;]%s[^;]%s[^;]%f[^';']%f[^';']%[^;]%[^;]%[^;]%[^;]"
As it stands, it looks for a space separated word, followed by a [, a ^, a ;, and a ] (which is self-contradictory; the character after the string is a space or end of string).
The first fixup would be to use scan-sets properly:
"%[^;]%[^;]%[^;]%[^;]%f[^';']%f[^';']%[^;]%[^;]%[^;]%[^;]"
Now you have a problem that the first %[^;] scans everything up to the end of string or first semicolon, leaving nothing for the second %[;] to match.
"%[^;]; %[^;]; %[^;]; %[^;]; %f[^';']%f[^';']%[^;]%[^;]%[^;]%[^;]"
This looks for a string up to a semicolon, then for the semicolon, then optional white space, then repeats for three items. Apart from adding a length to limit the size of string, preventing overflow, these are fine. The %f is OK. The following material looks for an odd sequence of characters again.
However, when the data is looked at, it seems to consist of a city, and then seven sets of 'a date plus three numbers'.
You'd do better with an array of structures (if you've worked with those yet), or a set of 4 parallel arrays, and a loop:
char jokeri[30];
char paiva[7][30];
float keskilampo[7];
float minlampo[7];
float maxlampo[7];
int eoc; // End of conversion
int offset = 0;
char sep;
if (fscanf(str + offset, "%29[^;]%c%n", jokeri, &sep, &eoc) != 2 || sep != ';')
...report error...
offset += eoc;
for (int i = 0; i < 7; i++)
{
if (fscanf(str + offset, "%29[^;];%f;%f;%f%c%n", paiva[i],
&keskilampo[i], &minlampo[i], &maxlampo[i], &sep, &eoc) != 5 ||
sep != ';')
...report error...
offset += eoc;
}
See also How to use sscanf() in loops.
Now you have data that can be managed. The set of 29 separately named variables is a ghastly thought; the code using them will be horrid.
Note that the scan-set conversion specifications limit the string to a maximum length one shorter than the size of jokeri and the paiva array elements.
You might legitimately be wondering about why the code uses %c%n and &sep before &eoc. There is a reason, but it is subtle. Suppose that the sscanf() format string is:
"%29[^;];%f;%f;%f;%n"
Further, suppose there's a problem in the data that the semicolon after the third number is missing. The call to sscanf() will report that it made 4 successful conversions, but it doesn't count the %n as an assignment, so you can't tell that sscanf() didn't find a semicolon and therefore did not set &eoc at all; the value is left over from a previous call to sscanf(), or simply uninitialized. By using the %c to scan a value into sep, we get 5 returned on success, and we can be sure the %n was successful too. The code checks that the value in sep is in fact a semicolon and not something else.
You might want to consider a space before the semi-colons, and before the %c. They'll allow some other data strings to be converted that would not be matched otherwise. Spaces in a format string (outside a scan-set) indicate where optional white space may appear.
I would use strtok function to break your string into pieces using ; as a delimiter. Such a long format string may be a source of problems in future.

How to write and read (including spaces) from text file

I'm using fscanf and fprintf.
I tried to delimit the strings on each line by \t and to read it like so:
fscanf(fp,"%d\t%s\t%s",&t->num,&t->string1,&t->string2);
The file contents:
1[TAB]string1[TAB]some string[NEWLINE]
It does not read properly. If I printf("%d %s %s",t->num,t->string1,t->string2) I get:
1 string1 some
Also I get this compile warning:
warning: format specifies type 'char *' but the argument has type 'char (*)[15]' [-Wformat]
How can I fix this without using binary r/w?
I'm guessing the space in "some string" is the problem. fscanf() reading a string using %s stops at the first whitespace character. To include spaces, use something like:
fscanf(fp, "%d\t%[^\n\t]\t%[^\n\t]", &t->num, &t->string1, &t->string2);
See also a reference page for fscanf() and/or another StackOverflow thread on reading tab-delimited items in C.
[EDIT in response to your edit: You seem to also have a problem with the arguments you're passing into fscanf(). You will need to post the declarations of t->string1 to be sure, but it looks like string1 is an array of characters, and therefore you should remove the & from the fscanf() call...]
The %s conversion specification stops reading at the first white space, and tabs and blanks both count as white space.
If you want to read a string of non-tabs, you can use a 'scan set' conversion specifier:
if (fscanf(fp, "%d\t%[^\t\n]\t%[^\t\n]", &t->num, t->string1, t->string2) != 3)
...oops - format error in input data...
(I'd lay odds that omitting the & from the string arguments is correct.) The question was edited; I win. Dropping the & is necessary to avoid the compiler warning!
This still doesn't quite do what you expect. If there are blanks at the start of the second field, they'll be eaten by the \t in the format string. Any white space in the format string eats any white space (including newlines) in the input. The %[^\t] conversion specification won't get started until there's a character that isn't white space in the input. I'm also assuming you want your input limited by newlines. You can leave out the \n characters if you prefer.
Note that I checked that the fscanf() interpreted 3 fields. It is important to error check your inputs.
If you really want control, you should probably read whole lines with fgets() and then use sscanf() to parse the data.
About fgets() and sscanf(); can you expand about how it will give more control?
Suppose the input data is written
1234
a string with spaces
another string
spread out over multiple lines like that. With raw fscanf(), this will be acceptable input even though it is spread over 9 lines of input. With fgets(), you can read a single line, and then analyze it with sscanf(), and you'll know that the first line was not in the correct format. You can then decide what to do about it.
Also, since mafso called me on it in his comment, we should ensure that there are no buffer overflows by limiting the size of the strings that the scan sets match.
if (fscanf(fp, "%d\t%14[^\t\n]\t%14[^\t\n]", &t->num, t->string1, t->string2) != 3)
...oops - format error in input data...
I'm using the error message about char (*)[15] to deduce that 14 is the correct number to use. Note that unlike printf(), you can't specify the sizes via * notation (in the scanf()-family, * supresses assignment), so you have to create the format with the correct sizes. Further, the size you specify is the number of characters before the terminating null byte, so if the array is of size 15, the size you specify in the format string is 14, as shown.

splitting string in c

I have a file where each line looks like this:
cc ssssssss,n
where the two first 'c's are individual characters, possibly spaces, then a space after that, then the 's's are a string that is 8 or 9 characters long, then there's a comma and then an integer.
I'm really new to c and I'm trying to figure out how to put this into 4 seperate variables per line (each of the first two characters, the string, and the number)
Any suggestions? I've looked at fscanf and strtok but i'm not sure how to make them work for this.
Thank you.
I'm assuming this is a C question, as the question suggests, not C++ as the tags perhaps suggest.
Read the whole line in.
Use strchr to find the comma.
Do whatever you want with the first two characters.
Switch the comma for a zero, marking the end of a string.
Call strcpy from the fourth character on to extract the sssssss part.
Call atoi on one character past where the comma was to extract the integer.
A string is a sequence of characters that ends at the first '\0'. Keep this in mind. What you have in the file you described isn't a string.
I presume n is an integer that could span multiple decimal places and could be negative. If that's the case, I believe the format string you require is "%2[^ ] %9[^,\n],%d". You'll want to pass fscanf the following expressions:
Your FILE *,
The format string,
An array of 3 chars silently converted to a pointer,
An array of 9 chars silently converted to a pointer,
... and a pointer to int.
Store the return value of fscanf into an int. If fscanf returns negative, you have a problem such as EOF or some other read error. Otherwise, fscanf tells you how many objects it assigned values into. The "success" value you're looking for in this case is 3. Anything else means incorrectly formed input.
I suggest reading the fscanf manual for more information, and/or for clarification.
fscanf function is very powerful and can be used to solve your task:
We need to read two chars - the format is "%c%c".
Then skip a space (just add it to the format string) - "%c%c ".
Then read a string until we hit a comma. Don't forget to specify max string size. So, the format is "%c%c %10[^,]". 10 - max chars to read. [^,] - list of allowed chars. ^, - means all except a comma.
Then skip a comma - "%c%c %10[^,],".
And finally read an integer - "%c%c %10[^,],%d".
The last step is to be sure that all 4 tokens are read - check fscanf return value.
Here is the complete solution:
FILE *f = fopen("input_file", "r");
do
{
char c1 = 0;
char c2 = 0;
char str[11] = {};
int d = 0;
if (4 == fscanf(f, "%c%c %10[^,],%d", &c1, &c2, str, &d))
{
// successfully got 4 values from the file
}
}
while(!feof(f));
fclose(f);

How To Read in Strings that only Contain Alphabet letters with fscanf?

I have been struggling to figure out the fscanf formatting. I just want to read in a file of words delimited by spaces. And I want to discard any strings that contain non-alphabetic characters.
char temp_text[100];
while(fscanf(fcorpus, "%101[a-zA-Z]s", temp_text) == 1) {
printf("%s\n", temp_text);
}
I've tried the above code both with and without the 's'. I read in another stackoverflow thread that the s when used like that will be interpreted as a literal 's' and not as a string. Either way - when I include the s and when I do not include the s - I can only get the first word from the file I am reading through to print out.
The %[ scan specifier does not skip leading spaces. Either add a space before it or at the end in place of your s. Also you have your 100 and 101 backwards and thus a serious buffer overflow bug.
The s isn't needed.
Here are a few things to try:
Print out the return value from fscanf, and make sure it is 1.
Make sure that the fscanf is consuming the whitespace by using fgetc to get the next character and printing it out.

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