C++ : Member reference base type 'char *' is not a structure or union

Question

void find_substring(char * str_for_search_in, char * substring)
{
    bool flag = false;
    for (int i = 0; i < strlen(str_for_search_in) - strlen(substring); i++)
    {
        if (str_for_search_in.substr(i, strlen(substring)) == substring)
        {
            cout << i << " ";
            flag = true;
            break;
        }
    }
    if (flag == false)
        cout << "NONE";
}

I am converting my program from C++ strings to C strings and stuck on this issue in line 6

What's the issue here?

It was length.substring everywhere previously, i changed them to strlen() so they fit char *

I've tried changing data types somewhere but that didn't work

Answer 1

For starters the function in C should be declared like

int find_substring( const char * str_for_search_in, const char * substring);

It does not change the passed strings so its parameters should be declared with the qualifier const. And the function should not output any message. It is the caller of the function will decide whether to output a message. The function just should return a value (0 or 1) that the caller of the function can check.

This for loop

for (int i = 0; i < strlen(str_for_search_in) - strlen(substring); i++)

at least has a wrong condition, You should write it like for example

for (int i = 0; i <= strlen(str_for_search_in) - strlen(substring); i++)

But this work only in case when strlen(str_for_search_in) is indeed greater than or equal to strlen(substring).

Also there are redundant calls of strlen.

Character arrays do not have member functions. So this expression

str_for_search_in.substr(i, strlen(substring))

is invalid.

And to compare strings in your for loop you need to use standard C string function strncmp declared in the header <string.h>.

Pay attention to that within your function you could use standard C string function strstr for example the following way

int find_substring( const char * str_for_search_in, const char * substring)
{
    return strstr( str_for_search_in, substring ) != NULL;
}