getline, getdelim - delimited string input

#include <stdio.h>
ssize_t getline(char **restrict lineptr, size_t *restrict n,
 FILE *restrict stream);
ssize_t getdelim(char **restrict lineptr, size_t *restrict n,
 int delim, FILE *restrict stream);

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

    Since glibc 2.10:
        _POSIX_C_SOURCE >= 200809L
    Before glibc 2.10:
        _GNU_SOURCE

getline() reads an entire line from stream, storing the address of the buffer containing the text into *lineptr. The buffer is null-terminated and includes the newline character, if one was found.

If *lineptr is set to NULL before the call, then getline() will allocate a buffer for storing the line. This buffer should be freed by the user program even if getline() failed.

Alternatively, before calling getline(), *lineptr can contain a pointer to a malloc(3)-allocated buffer *n bytes in size. If the buffer is not large enough to hold the line, getline() resizes it with realloc(3), updating *lineptr and *n as necessary.

In either case, on a successful call, *lineptr and *n will be updated to reflect the buffer address and allocated size respectively.

getdelim() works like getline(), except that a line delimiter other than newline can be specified as the delimiter argument. As with getline(), a delimiter character is not added if one was not present in the input before end of file was reached.

On success, getline() and getdelim() return the number of characters read, including the delimiter character, but not including the terminating null byte ('\0'). This value can be used to handle embedded null bytes in the line read.

Both functions return -1 on failure to read a line (including end-of-file condition). In the event of a failure, errno is set to indicate the error.

If *lineptr was set to NULL before the call, then the buffer should be freed by the user program even on failure.

#define _GNU_SOURCE
#include <stdio.h>
#include <stdlib.h>
int
main(int argc, char *argv[])
{
    FILE *stream;
    char *line = NULL;
    size_t len = 0;
    ssize_t nread;
    if (argc != 2) {
        fprintf(stderr, "Usage: %s <file>\n", argv[0]);
        exit(EXIT_FAILURE);
    }
    stream = fopen(argv[1], "r");
    if (stream == NULL) {
        perror("fopen");
        exit(EXIT_FAILURE);
    }
    while ((nread = getline(&line, &len, stream)) != -1) {
        printf("Retrieved line of length %zd:\n", nread);
        fwrite(line, nread, 1, stdout);
    }
    free(line);
    fclose(stream);
    exit(EXIT_SUCCESS);
}

read(2), fgets(3), fopen(3), fread(3), scanf(3)