How to find substring between quotation marks in C - c

Question

If I have a string such as the string that is the command
echo 'foobar'|cat
Is there a good way for me to get the text between the quotation marks ("foobar")? I read that it was possible to use scanf to do it in a file, is it also possible in-memory?
My attempt:
char * concat2 = concat(cmd, token);
printf("concat:%s\n", concat2);
int res = scanf(in, " '%[^']'", concat2);
printf("result:%s\n", in);

Answer 1

Use strtok() once, to locate the first occurrence of delimiter you wish (' in your case), and then once more, to find the ending pair of it, like this:
#include <stdio.h>
#include <string.h>
int main(void) {
const char* lineConst = "echo 'foobar'|cat"; // the "input string"
char line[256]; // where we will put a copy of the input
char *subString; // the "result"
strcpy(line, lineConst);
subString = strtok(line, "'"); // find the first double quote
subString=strtok(NULL, "'"); // find the second double quote
if(!subString)
printf("Not found\n");
else
printf("the thing in between quotes is '%s'\n", subString);
return 0;
}
Output:
the thing in between quotes is 'foobar'
I was based on this: How to extract a substring from a string in C?

Answer 2

If your string is in this format -"echo 'foobar'|cat", sscanf can be used-
char a[20]={0};
char *s="echo 'foobar'|cat";
if(sscanf(s,"%*[^']'%[^']'",a)==1){
// do something with a
}
else{
// handle this condition
}
%*[^'] will read and discard a string until it encounter single quote ' , the second format specifier %[^'] will read string till ' and store it in a.

Answer 3

There are a large number of ways to approach the problem. From walking a pair of pointers down the string to locate the delimiters, and a large number of string functions provided in string.h. You can make use of character search functions such as strchr or string search functions like strpbrk, you can use tokenizing functions like strtok, etc...
Look over and learn from them all. Here is an implementation with strpbrk and a pointer difference. It is non-destructive, so you need not make a copy of the original string.
#include <stdio.h>
#include <string.h>
int main (void) {
const char *line = "'foobar'|cat";
const char *delim = "'"; /* delimiter, single quote */
char *p, *ep;
if (!(p = strpbrk (line, delim))) { /* find the first quote */
fprintf (stderr, "error: delimiter not found.\n");
return 1;
}
p++; /* advance to next char */
ep = strpbrk (p, delim); /* set end pointer to next delim */
if (!p) { /* validate end pointer */
fprintf (stderr, "error: matching delimiters not found.\n");
return 1;
}
char substr[ep - p + 1]; /* storage for substring */
strncpy (substr, p, ep - p); /* copy the substring */
substr[ep - p] = 0; /* nul-terminate */
printf ("\n single-quoted string : %s\n\n", substr);
return 0;
}
Example Use/Output
$ ./bin/substr
single-quoted string : foobar
Without Using string.h
As mentioned above, you can also simply walk a pair of pointers down the string and locate your pairs of quotes in that manner as well. For completeness, here is an example finding multiple quoted strings within a single line:
#include <stdio.h>
int main (void) {
const char *line = "'foobar'|cat'mousebar'sum";
char delim = '\'';
char *p = (char *)line, *sp = NULL, *ep = NULL;
size_t i = 0;
for (; *p; p++) { /* for each char in line */
if (!sp && *p == delim) /* find 1st delim */
sp = p, sp++; /* set start ptr */
else if (!ep && *p == delim) /* find 2nd delim */
ep = p; /* set end ptr */
if (sp && ep) { /* if both set */
char substr[ep - sp + 1]; /* declare substr */
for (i = 0, p = sp; p < ep; p++)/* copy to substr */
substr[i++] = *p;
substr[ep - sp] = 0; /* nul-terminate */
printf ("single-quoted string : %s\n", substr);
sp = ep = NULL;
}
}
return 0;
}
Example Use/Output
$ ./bin/substrp
single-quoted string : foobar
single-quoted string : mousebar
Look all the answers over and let us know if you have any questions.