IO in C

October 16, 2022 1 minute read

Here lists several methods for input/output in C.

Methods and Examples

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

getline can be used for getting a line of input from a stream. It regards '\n' as the separator and stops with EOF. The string will include both null-terminated and the newline character. It will NOT regard space character and tab as the separator. For reading space separated input, check fscanf.
lineptr can be set as NULL or assigned with malloc. getline will malloc if lineptr is NULL or directly use/resize according to input length respectively. The address of the buffer pointer should be fed into getline because it may assign a new value to the pointer. The actual string size will be stored in n.
Remember to free the buffer afterwards.
More details about getline: getline(3) - Linux manual page (man7.org)

#include <stdio.h>
char *fgets(char *restrict s, int n, FILE *restrict stream);

fgets can be used for getting a line of input from a stream with maximum length limitation on the string. It regards '\n' as the separator and stops with EOF or maximum length limitation. The string will include both null-terminated and the newline character. Similar to getline, it does NOT regard space and tab as separator.
More details about fgets: fgets(3p) - Linux manual page (man7.org)

#include <stdio.h>
int fscanf(FILE *restrict stream, const char *restrict format, ...);

fscanf can be used for getting inputs from a stream with space, tab, newline as separators.
For string format, regular expression can be used.
When reading inputs from stdin, if several fscanf functions are sequentially placed, these functions will read until the input buffer becomes empty with no blocking.
More details about fscanf: fscanf(3p) - Linux manual page (man7.org)