strextract fails if search start is the same as the input string

[mdbartos]

The current code for strextract assumes the search start is shorter than the length of the input string.

If we want to extract a substring starting at the beginning of a string, we might want to use the input string as the search start string. However, this doesn't work for the current implementation due to:

        begin += strlen(search_start);

I can see reasons for both implementations; maybe we could include an argument that specifies the desired behavior.

[imondrag]

That's the defined behavior for strextract.

"Searches for the left-most c string in between search_start and search_end ..."

We shouldn't need to modify the existing implementation, you can use temporary buffers and strcat for the described behavior.

However, I would suggest the use of some pointer arithmetic to achieve your desired behavior:

char unparsed_string[] = "10:54pm Code 09 This is a test message\r";

// The string we want to search and keep.. with extra room for the parsed result
char parsed_error_code[ sizeof("Code ##") ] = "Code ";

// strextract returns the address of search_end on success,
// let's store the address of the space after the error code number
char *space_after_code = strextract(unparsed_string, 
            parsed_error_code + sizeof("Code ") - 1, /* The magic */
            parsed_error_code, " "); // Note the space

// Explanation: strextract only expects a pointer to a buffer that is large enough
// to store the parsed result. If we pass in a location later in the buffer, the
// function will treat that exactly like if it was the beginning of the buffer so to
// only modify the part that we want.. the ## location of the buffer. The -1 is 
// necessary because the sizeof operator includes the null character in c strings.

char parsed_error_msg[32] = {'\0'};

// Copy the message til the end
strextract(space_after_code, parsed_error_msg, " ", "\r"); 

printf("Error code: %s\n", parsed_error_code); // Error code: Code 09
printf("Message: %s\n", parsed_error_msg);     // Message: This is a test message