Remove character from array where spaces and punctuation marks are found

Question

In my program, I am checking whole cstring, if any spaces or punctuation marks are found, just add empty character to that location but the complilor is giving me an error: empty character constant.

Please help me out, in my loop i am checking like this

if(ispunct(str1[start])) {
    str1[start]=''; // << empty character constant. 
}
if(isspace(str1[start])) {
    str1[start]=''; // << empty character constant. 
}

This is where my errors are please correct me.

for eg the word is str,, ing, output should be string.

Answer 1

Try this (as you asked for cstring explicitly):

char str1[100] = "str,, ing";

if(ispunct(str1[start]) || isspace(str1[start])) {
    strncpy(str1 + start, str1 + start + 1, strlen(str1) - start + 1);
}

Well, doing this just in pure c language, there are more efficient solutions (have a look at @MichaelPlotke's answer for details).

But as you also explicitly ask for c++, I'd recommend a solution as follows:

Note you can use the standard c++ algorithms for 'plain' c-style character arrays also. You just have to place your predicate conditions for removal into a small helper functor and use it with the std::remove_if() algorithm:

struct is_char_category_in_question {
    bool operator()(const char& c) const;
};

And later use it like:

#include <string>
#include <algorithm>
#include <iostream>
#include <cctype>
#include <cstring>

// Best chance to have the predicate elided to be inlined, when writing 
// the functor like this:
struct is_char_category_in_question {
    bool operator()(const char& c) const {
        return std::ispunct(c) || std::isspace(c);
    }
};

int main() {
    static char str1[100] = "str,, ing";
    size_t size = strlen(str1);

    // Using std::remove_if() is likely to provide the best balance from perfor-
    // mance  and code size efficiency you can expect from your compiler 
    // implementation.
    std::remove_if(&str1[0], &str1[size + 1], is_char_category_in_question());

    // Regarding specification of the range definitions end of the above state-
    // ment, note we have to add 1 to the strlen() calculated size, to catch the 
    // closing `\0` character of the c-style string being copied correctly and
    // terminate the result as well!

    std::cout << str1 << endl; // Prints: string
}

See this compilable and working sample also here.