I have following problem:
// Basically I am reading from a file and storing in local array.
char myText[100] = "This is text of movie Jurassic Park";
// here I want to store each work in to dictionary
st.insert(&myText[0]); // should insert "This" not till end of sentence.
// similarly for next word "is", "text" and so on.
How do I do that in C?
For this, you would use the strtok function:
char myText[100] = "This is text of movie Jurassic Park";
char *p;
for (p = strtok(myText," "); p != NULL; p = strtok(NULL," ")) {
st.insert(p);
}
Note that this function modifies the string it's parsing by adding NUL bytes where the delimiters are.
You could use strtok(). http://www.cplusplus.com/reference/cstring/strtok/
For C you will need to include .
If you just want to split on spaces, you basically may want an strsplit or strtok.
Have a look at Split string with delimiters in C
Related
I want to use strtok and then return the string after the null terminator that strtok has placed.
char *foo(char *bar)
{
strtok(bar, " ");
return after_strtok_null(bar);
}
/*
examples:
foo("hello world") = "world"
foo("remove only the first") = "only the first"
*/
my code is not for skipping the first word (as I know a simple while loop will do) but I do want to use strtok once and then return the part that was not tokenized.
I will provide details of what I am trying to do at the end of the question, although I don't think it's really necessary
one solution that came into my mind was to simply skip all the null terminators until I reach a non - null:
char *foo(char *bar)
{
bar = strtok(bar, " ");
while(!(*(bar++)));
return bar;
}
This works fine for the examples shown above, but when it comes to using it on single words - I may misidentify the string's null terminator to be strtok's null terminator, and then I may access non - allocated memory.
For example, if I will try foo("demo"\* '\0' *\) the of strtok will be "demo"\* '\0' *\
and then, if I would run the while loop I will accuse the part after the string demo. another solution I have tried is to use strlen, but this one have the exact same problem.
I am trying to create a function that gets a sentence. some of the sentences have have their first word terminated with colons, although not necessarily. The function need to take the first word if it is terminated with colons and insert it (without the colons) into some global table. Then return the sentence without the first colons - terminated word and without the spaces that follow the word if the word has colons - terminated word at the start and otherwise, just return the sentence without the spaces in the start of the sentence.
You could use str[c]spn instead:
char *foo(char *bar) {
size_t pos = strcspn(bar, " ");
pos = strspn((bar += pos), "");
// *bar = '\0'; // uncomment to mimic strtok
return bar + pos;
}
You will get the expected substring of an empty string.
A good point is that you can avoid changing the original string - even if mimicing strtok is trivial...
I am trying to save one character and 2 strings into variables.
I use sscanf to read strings with the following form :
N "OldName" "NewName"
What I want : char character = 'N' , char* old_name = "OldName" , char* new_name = "NewName" .
This is how I am trying to do it :
sscanf(mystring,"%c %s %s",&character,old_name,new_name);
printf("%c %s %s",character,old_name,new_name);
The problem is , my problem stops working without any outputs .
(I want to ignore the quotation marks too and save only its content)
When you do
char* new_name = "NewName";
you make the pointer new_name point to the read-only string array containing the constant string literal. The array contains exactly 8 characters (the letters of the string plus the terminator).
First of all, using that pointer as a destination for scanf will cause scanf to write to the read-only array, which leads to undefined behavior. And if you give a string longer than 7 character then scanf will also attempt to write out of bounds, again leading to undefined behavior.
The simple solution is to use actual arrays, and not pointers, and to also tell scanf to not read more than can fit in the arrays. Like this:
char old_name[64]; // Space for 63 characters plus string terminator
char new_name[64];
sscanf(mystring,"%c %63s %63s",&character,old_name,new_name);
To skip the quotation marks you have a couple of choices: Either use pointers and pointer arithmetic to skip the leading quote, and then set the string terminator at the place of the last quote to "remove" it. Another solution is to move the string to overwrite the leading quote, and then do as the previous solution to remove the last quote.
Or you could rely on the limited pattern-matching capabilities of scanf (and family):
sscanf(mystring,"%c \"%63s\" \"%63s\"",&character,old_name,new_name);
Note that the above sscanf call will work iff the string actually includes the quotes.
Second note: As said in the comment by Cool Guy, the above won't actually work since scanf is greedy. It will read until the end of the file/string or a white-space, so it won't actually stop reading at the closing double quote. The only working solution using scanf and family is the one below.
Also note that scanf and family, when reading string using "%s" stops reading on white-space, so if the string is "New Name" then it won't work either. If this is the case, then you either need to manually parse the string, or use the odd "%[" format, something like
sscanf(mystring,"%c \"%63[^\"]\" \"%63[^\"]\"",&character,old_name,new_name);
You must allocate space for your strings, e.g:
char* old_name = malloc(128);
char* new_name = malloc(128);
Or using arrays
char old_name[128] = {0};
char new_name[128] = {0};
In case of malloc you also have to free the space before the end of your program.
free(old_name);
free(new_name);
Updated:...
The other answers provide good methods of creating memory as well as how to read the example input into buffers. There are two additional items that may help:
1) You expressed that you want to ignore the quotation marks too.
2) Reading first & last names when separated with space. (example input is not)
As #Joachim points out, because scanf and family stop scanning on a space with the %s format specifier, a name that includes a space such as "firstname lastname" will not be read in completely. There are several ways to address this. Here are two:
Method 1: tokenizing your input.
Tokenizing a string breaks it into sections separated by delimiters. Your string input examples for instance are separated by at least 3 usable delimiters: space: " ", double quote: ", and newline: \n characters. fgets() and strtok() can be used to read in the desired content while at the same time strip off any undesired characters. If done correctly, this method can preserve the content (even spaces) while removing delimiters such as ". A very simple example of the concept below includes the following steps:
1) reading stdin into a line buffer with fgets(...)
2) parse the input using strtok(...).
Note: This is an illustrative, bare-bones implementation, sequentially coded to match your input examples (with spaces) and includes none of the error checking/handling that would normally be included.
int main(void)
{
char line[128];
char delim[] = {"\n\""};//parse using only newline and double quote
char *tok;
char letter;
char old_name[64]; // Space for 63 characters plus string terminator
char new_name[64];
fgets(line, 128, stdin);
tok = strtok(line, delim); //consume 1st " and get token 1
if(tok) letter = tok[0]; //assign letter
tok = strtok(NULL, delim); //consume 2nd " and get token 2
if(tok) strcpy(old_name, tok); //copy tok to old name
tok = strtok(NULL, delim); //consume 3rd " throw away token 3
tok = strtok(NULL, delim); //consume 4th " and get token 4
if(tok) strcpy(new_name, tok); //copy tok to new name
printf("%c %s %s\n", letter, old_name, new_name);
return 0;
}
Note: as written, this example (as do most strtok(...) implementations) require very narrowly defined input. In this case input must be no longer than 127 characters, comprised of a single character followed by space(s) then a double quoted string followed by more space(s) then another double quoted string, as defined by your example:
N "OldName" "NewName"
The following input will also work in the above example:
N "old name" "new name"
N "old name" "new name"
Note also about this example, some consider strtok() broken, while others suggest avoiding its use. I suggest using it sparingly, and only in single threaded applications.
Method 2: walking the string.
A C string is just an array of char terminated with a NULL character. By selectively copying some characters into another string, while bypassing the one you do not want (such as the "), you can effectively strip unwanted characters from your input. Here is an example function that will do this:
char * strip_ch(char *str, char ch)
{
char *from, *to;
char *dup = strdup(str);//make a copy of input
if(dup)
{
from = to = dup;//set working pointers equal to pointer to input
for (from; *from != '\0'; from++)//walk through input string
{
*to = *from;//set destination pointer to original pointer
if (*to != ch) to++;//test - increment only if not char to strip
//otherwise, leave it so next char will replace
}
*to = '\0';//replace the NULL terminator
strcpy(str, dup);
free(dup);
}
return str;
}
Example use case:
int main(void)
{
char line[128] = {"start"};
while(strstr(line, "quit") == NULL)
{
printf("Enter string (\"quit\" to leave) and hit <ENTER>:");
fgets(line, 128, stdin);
sprintf(line, "%s\n", strip_ch(line, '"'));
printf("%s", line);
}
return 0;
}
I'm trying to do split some strings by {white_space} symbol.
btw, there is a problem within some splits. which means, I want to split by {white_space} symbol but also quoted sub-strings.
example,
char *pch;
char str[] = "hello \"Stack Overflow\" good luck!";
pch = strtok(str," ");
while (pch != NULL)
{
printf ("%s\n",pch);
pch = strtok(NULL, " ");
}
This will give me
hello
"Stack
Overflow"
good
luck!
But What I want, as you know,
hello
Stack Overflow
good
luck!
Any suggestion or idea please?
You'll need to tokenize twice. The program flow you currently have is as follows:
1) Search for space
2) Print all characters prior to space
3) Search for next space
4) Print all characters between last space, and this one.
You'll need to start thinking in a different matter, two layers of tokenization.
Search for Quotation Mark
On odd-numbered strings, perform your original program (search for spaces)
On even-numbered strings, print blindly
In this case, even numbered strings are (ideally) within quotes. ab"cd"ef would result in ab being odd, cd being even... etc.
The other side, is remembering what you need to do, and what you're actually looking for (in regex) is "[a-zA-Z0-9 \t\n]*" or, [a-zA-Z0-9]+. That means the difference between the two options, are whether it's separated by quotes. So separate by quotes, and identify from there.
Try altering your strategy.
Look at non-white space things, then when you find quoted string you can put it in one string value.
So, you need a function that examines characters, between white space. When you find '"' you can change the rules and hoover everything up to a matching '"'. If this function returns a TOKEN value and a value (the string matched) then what calls it, can decide to do the correct output. Then you have written a tokeniser, and there actually exist tools to generate them called "lexers" as they are used widely, to implement programming languages/config files.
Assuming nextc reads next char from string, begun by firstc( str) :
for (firstc( str); ((c = nextc) != NULL;) {
if (isspace(c))
continue;
else if (c == '"')
return readQuote; /* Handle Quoted string */
else
return readWord; /* Terminated by space & '"' */
}
return EOS;
You'll need to define return values for EOS, QUOTE and WORD, and a way to get the text in each Quote or Word.
Here's the code that works... in C
The idea is that you first tokenize the quote, since that's a priority (if a string is inside the quotes than we don't tokenize it, we just print it). And for each of those tokenized strings, we tokenize within that string on the space character, but we do it for alternate strings, because alternate strings will be in and out of the quotes.
#include <stdio.h>
#include <string.h>
#include <stdbool.h>
int main() {
char *pch1, *pch2, *save_ptr1, *save_ptr2;
char str[] = "hello \"Stack Overflow\" good luck!";
pch1 = strtok_r(str,"\"", &save_ptr1);
bool in = false;
while (pch1 != NULL) {
if(in) {
printf ("%s\n", pch1);
pch1 = strtok_r(NULL, "\"", &save_ptr1);
in = false;
continue;
}
pch2 = strtok_r(pch1, " ", &save_ptr2);
while (pch2 != NULL) {
printf ("%s\n",pch2);
pch2 = strtok_r(NULL, " ", &save_ptr2);
}
pch1 = strtok_r(NULL, "\"", &save_ptr1);
in = true;
}
}
References
Tokenizing multiple strings simultaneously
http://linux.die.net/man/3/strtok_r
http://www.cplusplus.com/reference/cstring/strtok/
Just got a question regards, when you read lines of text from a text file how would you separate the words and store them into an array.
For example if I have two lines of text in my text file that looks like this:
1005; AndyCool; Andy; Anderson; 23; LA
1006; JohnCool; John; Anderson; 23; LA
How would you split them into based on the ';' .
And then store them in 2D array.
Sorry I haven't started my coding just yet to paste it here
Cheers ...
Use the strsep function:
char* token;
char* line;
/* I assume the line as loaded from file */;
if( line != NULL ) {
while ((token = strsep(&line, ";")) != NULL)
{
/*
token points to the current extracted string,
use it to fill your array
*/
}
}
First read using fgets, then use strtok to split a string http://www.cplusplus.com/reference/cstring/strtok/
Look at the manual pages for fopen, fgets, strstr and and strchr and strspn functions ... The strtok and strsep functions also work for most things you will do.
i have a string of the format "ABCDEFG,12:34:56:78:90:11". i want to separate these two values that are separated by commas into two different strings. how do i do that in gcc using c language.
One possibility is something like this:
char first[20], second[20];
scanf("%19[^,], %19[^\n]", first, second);
So many people are suggesting strtok... Why? strtok is a left-over of stone age of programming and is good only for 20-line utilities!
Each call to strtok modifies strToken by inserting a null character after the token returned by that call. [...]
[F]unction uses a static variable for parsing the string into tokens. [...] Interleaving calls to this function is highly likely to produce data corruption and inaccurate results.
scanf, as in Jerry Coffin's answer, is a much better alternative. Or, you can do it manually: find the separator with strchr, then copy parts to separate buffers.
char str[] = "ABCDEFG,12:34:56:78:90:11"; //[1]
char *first = strtok(str, ","); //[2]
char *second = strtok(NULL, ""); //[3]
[1] ABCDEFG,12:34:56:78:90:11
[2] ABCDEFG\012:34:56:78:90:11
Comma replaced with null character with first pointing to 'A'
[3] Subsequent calls to `strtok` have NULL` as first argument.
You can change the delimiter though.
Note: you cannot use "string literals", because `strtok` modifies the string.
You can use strtok which will allow you to specify the separator and generate the tokens for you.
You could use strtok:
Example from cppreference.com:
char str[] = "now # is the time for all # good men to come to the # aid of their country";
char delims[] = "#";
char *result = NULL;
result = strtok( str, delims );
while( result != NULL ) {
printf( "result is \"%s\"\n", result );
result = strtok( NULL, delims );
}
Try using the following regex it will find anything with chars a-z A-Z followed by a ","
"[A-Z]," if you need lower case letter too try "[a-zA-Z],"
If you need it to search for the second part first you could try the following
",[0-9]{2}:[0-9]{2}:[0-9]{2}:[0-9]{2}:[0-9]{2}:[0-9]{2}"
There is an example on how to use REGEX's at
http://ddj.com/184404797
Thanks,
V$h3r