C string handling function to get substring [closed] - c++

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I remenber a function in C or C++ that can do something like this:
string = "Hello my name is: 1234567 have a good day!"
function(string, "Hello my name is: %s have a good day!", substring)
and substring would be 1234567. What function is that?

Answer 1

In C, you can do that with sscanf(). Of course, there is no string datatype in C, though:
#include <stdio.h>
int main(void)
{
const char string[] = "Hello my name is: 1234567 have a good day!";
char substring[32];
if(sscanf(string, "Hello my name is: %31s have a good day!", substring) == 1)
{
printf("got '%s'\n", substring);
}
return 0;
}

Answer 2

sscanf is the function that you search.

Answer 3

It seems like you are trying to extract the number and not really so much the substring.
If your prefix string always begins with the format: "Hello my name is: " You can do:
const auto size = strlen("Hello my name is: ");
int substring = stoi(string.substr(size));
If you are unsure of your prefix, then I'd recommend a regex:
smatch m;
regex_search(string, m, regex(".*?(-?\\d+)"));
int substring = stoi(m[1]);

Answer 4

You may be looking for sscanf, but you probably want C++ regular expressions.
Start with a std::regex:
std::regex re( "Hello my name is: \b(\w+)\b have a good day!" );
Then put it into a function:
std::string get_name( std::string const& src ) {
static std::regex re( R"-(Hello my name is: (\w+) have a good day!)-" );
std::smatch results;
bool bworked = std::regex_match( src, results, re );
if (!bworked) return {};
// Assert(results.size() >= 2);
if (results.size() < 2) return {};
return results.str(1);
}
This gives you a lot more control than sscanf with only a bit more work.
live example
Going beyond regular expressions reaches full on parsing.
This solution uses C++11 features. Some compilers have <regex> headers that are basically stubs as well, so check compiler support.