string::find_first_not_of Problem... (C++)

[PirateMcplunder]

I am working on a program that involves a lot of string manipulation and after many hours of beating my head against the wall I cannot seem to figure out what is wrong with my use of the string::find_first_not_of function.

I have string::find working fine throughout the program but I cannot seem to get string::find_first_not_of to work properly.

I am attempting to identify whether or not the string before_token contains only digits and/or spaces/tabs. The input I am using does indeed only contain digits and a tab but I still end up seeing my error message every time.

The input line looks like this:
2 #number of hops
(the space between 2 and # is a tab)

Here is a snippit of the code that is not working. I can provide the rest if there isn't anything visibly wrong with this.


size_t found;
string first_input_line;
string before_token;

/* WORKS */

/* check first line for reference to the number of hops. */
found=first_input_line.find("number of hops");
if (found==string::npos){
cerr << "No explicit reference to \"number of hops\" found in the comment for first input line." << endl;
cerr << usage << endl;
exit(1);
}


/* get first input line up to token "#" */
getline(input_buffer, before_token, '#');

/* DOESN'T WORK */

/* check first part of first line for integer type. */
found=before_token.find_first_not_of("0123456789 \t");
if (found==string::npos){
cerr << "Integer not found for the number of hops. Please check input:\n" << endl;
cerr << usage << endl;
exit (1);
}


Any help or hints would be greatly appreciated. I really don't want to keep having to comment out my error checking code because I don't understand it.

I believe I am following correct form (see: http://www.cplusplus.com/reference/string/string/find_first_not_of/). What am I missing?
Thank you.

[GeneralZod]

before_token.find_first_not_of("0123456789 \t");


You don't seem to be doing anything with the return value.

[PirateMcplunder]

before_token.find_first_not_of("0123456789 \t");


You don't seem to be doing anything with the return value.
Sorry, I pasted in the code wrong. I can't get the code to work even with:

found=before_token.find_first_not_of("0123456789 \t");

I changed the code in the original post to reflect this. Any thoughts on why it wouldn't be working even when I am assigning the return value correctly?

[GeneralZod]

There's a bunch of other code missing (input_buffer's declaration; first_input_line; etc) but I'm a bit perplexed as to what it's supposed to do.

What is the value of before_token before you call find_first_not_of? I'm guessing it's supposed to be

2<tab>

in which case before_token.find_first_not_of("0123456789 \t") should be npos.

Please post a compileable and runnable version :)

Edit: VV

Cool :)

[PirateMcplunder]

you are correct! == should be !=

Thank you!