1FGETS(3P) POSIX Programmer's Manual FGETS(3P)
2
6 This manual page is part of the POSIX Programmer's Manual. The Linux
7 implementation of this interface may differ (consult the corresponding
8 Linux manual page for details of Linux behavior), or the interface may
9 not be implemented on Linux.
10
13 fgets — get a string from a stream
14
16 #include <stdio.h>
17 char *fgets(char *restrict s, int n, FILE *restrict stream);
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21 The functionality described on this reference page is aligned with the
22 ISO C standard. Any conflict between the requirements described here
23 and the ISO C standard is unintentional. This volume of POSIX.1‐2008
24 defers to the ISO C standard.
25 The fgets() function shall read bytes from stream into the array
27 pointed to by s, until n−1 bytes are read, or a <newline> is read and
28 transferred to s, or an end-of-file condition is encountered. The
29 string is then terminated with a null byte.
30 The fgets() function may mark the last data access timestamp of the
32 file associated with stream for update. The last data access timestamp
33 shall be marked for update by the first successful execution of
34 fgetc(), fgets(), fread(), fscanf(), getc(), getchar(), getdelim(),
35 getline(), gets(), or scanf() using stream that returns data not sup‐
36 plied by a prior call to ungetc().
37
39 Upon successful completion, fgets() shall return s. If the stream is
40 at end-of-file, the end-of-file indicator for the stream shall be set
41 and fgets() shall return a null pointer. If a read error occurs, the
42 error indicator for the stream shall be set, fgets() shall return a
43 null pointer, and shall set errno to indicate the error.
44
46 Refer to fgetc().
47 The following sections are informative.
49
51 Reading Input
52 The following example uses fgets() to read lines of input. It assumes
53 that the file it is reading is a text file and that lines in this text
54 file are no longer than 16384 (or {LINE_MAX} if it is less than 16384
55 on the implementation where it is running) bytes long. (Note that the
56 standard utilities have no line length limit if sysconf(_SC_LINE_MAX)
57 returns −1 without setting errno. This example assumes that
58 sysconf(_SC_LINE_MAX) will not fail.)
59 #include <limits.h>
61 #include <stdio.h>
62 #include <unistd.h>
63 #define MYLIMIT 16384
64 char *line;
66 int line_max;
67 if (LINE_MAX >= MYLIMIT) {
68 // Use maximum line size of MYLIMIT. If LINE_MAX is
69 // bigger than our limit, sysconf() can't report a
70 // smaller limit.
71 line_max = MYLIMIT;
72 } else {
73 long limit = sysconf(_SC_LINE_MAX);
74 line_max = (limit < 0 || limit > MYLIMIT) ? MYLIMIT : (int)limit;
75 }
76 // line_max + 1 leaves room for the null byte added by fgets().
78 line = malloc(line_max + 1);
79 if (line == NULL) {
80 // out of space
81 ...
82 return error;
83 }
84 while (fgets(line, line_max + 1, fp) != NULL) {
86 // Verify that a full line has been read ...
87 // If not, report an error or prepare to treat the
88 // next time through the loop as a read of a
89 // continuation of the current line.
90 ...
91 // Process line ...
92 ...
93 }
94 free(line);
95 ...
96
98 None.
99
101 None.
102
104 None.
105
107 Section 2.5, Standard I/O Streams, fgetc(), fopen(), fread(), fscanf(),
108 getc(), getchar(), getdelim(), gets(), ungetc()
109 The Base Definitions volume of POSIX.1‐2008, <stdio.h>
111
113 Portions of this text are reprinted and reproduced in electronic form
114 from IEEE Std 1003.1, 2013 Edition, Standard for Information Technology
115 -- Portable Operating System Interface (POSIX), The Open Group Base
116 Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
117 cal and Electronics Engineers, Inc and The Open Group. (This is
118 POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) In the
119 event of any discrepancy between this version and the original IEEE and
120 The Open Group Standard, the original IEEE and The Open Group Standard
121 is the referee document. The original Standard can be obtained online
122 at http://www.unix.org/online.html .
123 Any typographical or formatting errors that appear in this page are
125 most likely to have been introduced during the conversion of the source
126 files to man page format. To report such errors, see https://www.ker‐
127 nel.org/doc/man-pages/reporting_bugs.html .
128IEEE/The Open Group 2013 FGETS(3P)