lineptr

Lineptr is a conventional parameter name used in the POSIX getline and related functions to refer to a buffer that will hold a line read from a stream. The name does not denote a separate type or object; it is simply the pointer to the memory that stores the line text.

In C, the getline function has the signature ssize_t getline(char **lineptr, size_t *n, FILE *stream). The lineptr argument points to a buffer that will contain the input line, and n points to the size of that buffer. If *lineptr is NULL or *n is 0, getline allocates a buffer with malloc and stores the address in *lineptr, updating *n to reflect the buffer size. If the existing buffer is large enough, getline uses it; otherwise it reallocates as needed.

The function reads from the specified stream up to and including the newline character, or until end-of-file, and stores the result as a null-terminated string in *lineptr. It returns the number of characters read, including the newline if present, but not including the terminating null byte. On end-of-file with no characters read, or on error, it returns -1. When successful, the caller owns the allocated buffer and is responsible for freeing it with free(*lineptr) when it is no longer needed. Subsequent calls can reuse the same buffer by passing the same lineptr and n.

Lineptr is often discussed alongside getdelim, which reads up to a specified delimiter rather than a newline. The term emphasizes the buffer’s role rather than a distinct data type, and while getline is common on many systems, portability varies across platforms.