getline

getline is a line-oriented input facility used to read an entire line from a stream into a dynamically allocated buffer. In C, getline refers to a POSIX/GNU extension that may not be available on all platforms. In C++, the standard library provides a separate function, std::getline, used to extract a line from a stream into a string.

In C, the POSIX getline function has the prototype ssize_t getline(char **lineptr, size_t *n, FILE *stream). It reads from stream until a newline or end-of-file is encountered. The newline is stored in the buffer. If *lineptr is NULL, getline allocates memory with malloc; otherwise it may realloc as needed. On return, *lineptr points to a null-terminated buffer, *n is the buffer size, and the function returns the number of characters read, including the delimiter. If no characters are read before EOF or an error occurs, it returns -1. The caller must free *lineptr when finished.

In C++, std::getline reads from an input stream into a std::string (or another character sequence) until the newline delimiter is found. The newline is extracted but not stored in the string. It does not require manual memory management. There are variants that allow specifying a different delimiter or a different output container.

Portability and usage notes: getline is not part of ISO C, so portable C code often uses fgets or related functions; POSIX environments provide it. In C++, std::getline is widely supported across standard library implementations. When using the C version, include the appropriate headers and manage the allocated buffer; in C++, memory management is handled by std::string.