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getline, getwline, getdelim, getwdelim

From cppreference.com
< c‎ | experimental‎ | dynamic
 
C
 
Technical Specifications
 
Dynamic memory extensions
 
Defined in header <stdio.h>
ssize_t getline(char **lineptr, size_t *n, FILE *stream);
 (1) (dynamic memory TR)
ssize_t getwline(wchar_t **lineptr, size_t *n, FILE *stream);
 (2) (dynamic memory TR)
ssize_t getdelim(char ** restrict lineptr, size_t * restrict n,
                 int delimiter, FILE *stream);
 (3) (dynamic memory TR)
ssize_t getwdelim(wchar_t ** restrict lineptr, size_t * restrict n,
                 wint_t delimiter, FILE * stream);
 (4) (dynamic memory TR)
1) Behaves like getdelim(lineptr, n, '\n', stream)
2) Behaves like getwdelim(lineptr, n, L'\n', stream)
3) Reads from the stream stream as if by fgetc, until delimiter is encountered, storing the characters in the buffer of size *n pointed to by *lineptr, automatically increasing its size as if by realloc to fit the entire input, including the delimiter, and adding a null terminator. The pointer returned by realloc is written back into *lineptr. *lineptr may be null, in which case previous value of *n is ignored and getline allocates a new buffer as if by malloc. In any case the final length of the allocated buffer is written to *n. The behavior is undefined if delimiter has a value that is outside the range of unsigned char or EOF.
4) Same as (3), except the characters are read as if by fgetwc and that delimiter must be a valid wchar_t or WEOF.

If *lineptr is not null, the behavior is undefined if *lineptr is not a pointer that can be passed to free or if *n is greater than the size of the allocated memory pointed to by *lineptr. The behavior is also undefined if n is not a valid pointer suitable for writing a value of type size_t.

As all functions from Dynamic Memory TR, getline is only guaranteed to be available if __STDC_ALLOC_LIB__ is defined by the implementation and if the user defines __STDC_WANT_LIB_EXT2__ to the integer constant 1 before including stdio.h.

Contents

[edit] Parameters

lineptr - pointer to a pointer to the initial buffer or to a null pointer
n - pointer to the size of the initial buffer
delimiter - the delimiter character
stream - valid input stream, opened by fopen

[edit] Return value

The number of characters stored in the buffer, including the delimiter, but excluding the null terminator.

On error, returns -1 and sets feof or ferror on stream.

[edit] Notes

These functions are identical to their POSIX versions except that it is allowed, but not required to set errno on error.

[edit] Example

Run this code
#ifdef __STDC_ALLOC_LIB__
#define __STDC_WANT_LIB_EXT2__ 1
#else
#define _POSIX_C_SOURCE 200809L
#endif
 
#include <stdio.h>
#include <stdlib.h>
void get_y_or_n(void)
{
    char *response = NULL;
    size_t len;
    printf("Continue? [y] n: ");
    if((getline(&response, &len, stdin) < 0) || (len && response[0] == 'n')) {
        free(response);
        exit(0);
    }
    free(response);
    return;
}
int main(void) 
{
    get_y_or_n();
}

Output: 

Continue? [y] n:

[edit] See also

 gets a character string from a file stream
(function) [edit]
(removed in C11)(C11)
 reads a character string from stdin
(function) [edit]
(C95)
 gets a wide string from a file stream
(function) [edit]
allocates memory
(function) [edit]
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