C++ - Replace spaces with %20

Question

I am looking for a way to prepare a string for use as a URL.

The basics of the code is you type in what you are looking for and it opens a browser with what you typed in. I am learning C++, so this is a learning program. And please be as specific as possible for I am new to C++.

Here is what I am trying to do:

cin >> s_input;
transform(s_input.begin(), s_input.end(), s_input.begin(), tolower);
s_input = "start http://website.com/" + s_input + "/0/7/0";
system(s_input.c_str());

But I am trying to replace all the spaces the user enter with a '%20'. I have found one method this way but it only works with one letter at a time, and I am needing to do it with a full string and not an array of chars. Here is the method I have tried:

cin >> s_input;
transform(s_input.begin(), s_input.end(), s_input.begin(), tolower);
using std::string;
using std::cout;
using std::endl;
using std::replace;
replace(s_input.begin(), s_input.end(), ' ', '%20');
s_input = "start http://website.com/" + s_input + "/0/7/0";
system(s_input.c_str());

Thanks for your help!

What you're actually trying to do is escape all special characters in a string. Space is not the only character illegal in URLs. — Wug, Jul 18 '12 at 03:59
For basic "find and replace" on strings, see [this question](http://stackoverflow.com/q/3418231/501250). But you should really consider using a third-party library to properly URI-encode the string instead. — cdhowie, Jul 18 '12 at 04:01
@wug You are correct about that. But this is simply a learning program and I can only take it one step at a time. I will be the only one using this.. — alexander7567, Jul 18 '12 at 04:01

Some programmer dude · Accepted Answer · 2012-07-19T05:40:32.647

5

If you have Visual Studio 2010 or later you should be able to use regular expressions to search/replace:

std::regex space("[[:space:]]");
s_input = std::regex_replace(s_input, space, "%20");

Edit: How to use the six-argument version of std::regex_replace:

std::regex space("[[:space:]]");
std::string s_output;
std::regex_replace(s_output.begin(), s_input.begin(), s_input.end(), space, "%20");

The string s_output now contains the changed string.

You might have to change the replacement string to std::string("%20").

As you see I have only five arguments, that's because the sixth should have a default value.

edited Jul 19 '12 at 05:40

answered Jul 18 '12 at 05:54

Some programmer dude

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EDIT: Found you must also "#include ". Found this by visiting the link – alexander7567 Jul 18 '12 at 20:15
OK, i tried this method and it gives me this error: "No instance of overloaded function std::regex_replace matches the argument list" and it also gives me "expects 6 arguments - 3 provided" – alexander7567 Jul 18 '12 at 20:44
@alexander7567 Added example showing how to use the six-argument version of the function. – Some programmer dude Jul 19 '12 at 05:41

score 1 · Answer 2 · answered Jul 18 '12 at 04:36

std::replace is only able to replace single elements (chars in this case) with single elements. You are trying to replace a single element with three. You will need a special function to do that. Boost has one, called replace_all, you can use it like this:

boost::replace_all(s_input, " ", "%20");

score 0 · Answer 3 · answered Jul 18 '12 at 04:14

0

If you google: C++ UrlEncode, you will find many hits. Here's one:

http://www.zedwood.com/article/111/cpp-urlencode-function

answered Jul 18 '12 at 04:14

Steve Wellens

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C++ - Replace spaces with %20

3 Answers3