Which function allows you to read in an entire line of text at once?

The function that allows you to read in an entire line of text at once is getline. This function is specifically designed to capture a complete line of input, including spaces, until a newline character is encountered. This makes it particularly useful for handling user input where there are multiple words or phrases that need to be read together as a single line.

getline works well for managing input because it dynamically allocates memory to hold the entire string, thus allowing it to adapt to different lengths of input without requiring the programmer to specify a maximum size in advance explicitly. This is a key feature that distinguishes it from other functions, which may not handle spaces or may require prior knowledge of the input size.

In contrast, the other provided options are primarily used for reading formatted input or data of a specific type: cin and scanf are meant for reading data separated by whitespace or formatted according to specific types, while printf is used for outputting data rather than inputting it. Thus, getline is the suitable choice for reading an entire line of text.