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C++ istream::readsome() function

The C++ std::istream::readsome() function is used to read the specific number of characters from a input stream into a buffer, without blocking. It reads up to the specified limit or the number of available characters, whichever is smaller.

Unlike read(), which waits to fill the buffer completely, readsome() returns immediately with the available data.

Following is the syntax for std::istream::readsome() function.

streamsize readsome (char* s, streamsize n);

• s − It indicates the pointer to an array where the extracted characters are stored.
• n − It indicates the maximum number of characters to extract.

This function returns the number of characters stored.

If an exception is thrown, the object is in a valid state.

Modifies the elements in the array pointed by s and the stream object.

Let's look at the following example, where we are going to consider the bsic usage of readsome() function.

#include <iostream>
#include <sstream>
int main()
{
    std::istringstream x("Tp, TutorialsPoint");
    char a[5];
    x.readsome(a, 4);
    a[5] = '\0';
    std::cout << "Result : " << a << std::endl;
    return 0;
}

Output of the above code is as follows −

Result : Tp, 

Consider the following example, where we are going to read partial data from std::istringstream.

#include <iostream>
#include <sstream>
int main()
{
    std::istringstream a("Hello Namaste");
    char b[6];
    a.readsome(b, sizeof(b) - 1);
    b[a.gcount()] = '\0';
    std::cout << "First read: " << b << std::endl;
    a.readsome(b, sizeof(b) - 1);
    b[a.gcount()] = '\0';
    std::cout << "Second read: " << b << std::endl;
    return 0;
}

Following is the output of the above code −

First read: Hello
Second read:  Nama

istream.htm

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