标准IO库函数复习

打开文件，打开文件一定要成对写，养成好习惯很重要。比如 fopen()fclose
<ol>
<li>fopen()</li>

<pre lang="c" escaped="true">
/* fopen() */
FILE *fopen(const char *path, const char *mode);

FILE *fdopen(int fd, const char *mode);

FILE *freopen(const char *path, const char *mode, FILE *stream);
</pre>

mode:

<strong>r</strong> Open text file for reading. The stream is positioned at the beginning of the file.

<strong>r+</strong> Open for reading and writing. The stream is positioned at the beginning of the file.

<strong>w</strong> Truncate file to zero length or create text file for writing. The stream is positioned at the beginning of the file.

<strong>w+</strong> Open for reading and writing. The file is created if it does not exist, otherwise it is truncated. The stream is positioned at the beginning of the
file.

<strong>a</strong> Open for appending (writing at end of file). The file is created if it does not exist. The stream is positioned at the end of the file.

<strong>a+</strong> Open for reading and appending (writing at end of file). The file is created if it does not exist. The initial file position for reading is at the
beginning of the file, but output is always appended to the end of the file.

&nbsp;
&nbsp;

<li>fclose()</li>

<pre lang="c" escaped="true">
/* fclose() */
int fclose(FILE *stream);
</pre>

RETURN VALUE
Upon successful completion 0 is returned. Otherwise, EOF is returned and errno is set to indicate the error. In either case any further access (including
another call to fclose()) to the stream results in undefined behavior.

<li>EOF</li>

<pre lang="c" escaped="true">
/* End of file character.
* some things throughout the library rely on this being -1. */
#ifndef EOF
#define EOF (-1)
#endif

/* stdin/stdout/stderr */
stdin
stdout
stderr
</pre>

<li>errno</li>

<pre lang="c" escaped="true">
/* errno */
void perror(const char *s);
char *strerror(int errnum);

int strerror_r(int errnum, char *buf, size_t buflen);
/* XSI-compliant */

char *strerror_r(int errnum, char *buf, size_t buflen);
/* GNU-specific */

char *strerror_l(int errnum, locale_t locale);

fprintf(stderr, "filename:%s, line %d: %s.\n", __FILE__, __LINE__, strerror(errno));
</pre>

<li>fgetc() fputc()</li>

<pre lang="c" escaped="true">
/* get char */
int fgetc(FILE *stream);

char *fgets(char *s, int size, FILE *stream);

int getc(FILE *stream);

int getchar(void);

int ungetc(int c, FILE *stream);

/* put char */
int fputc(int c, FILE *stream);

int fputs(const char *s, FILE *stream);

int putc(int c, FILE *stream);

int putchar(int c);

int puts(const char *s);
</pre>

举个例子如下：
<pre lang="c" escaped="true">
#include <stdio.h>
#include <stdlib.h>

int main(void)
{
FILE *fp;
int ch;

if ((fp = fopen("test2", "w+")) == NULL)
{
perror("Open file test2.\n");
exit(1);
}

while ((ch = getchar()) != EOF)
fputc(ch, fp);
rewind(fp);
while((ch = fgetc(fp)) != EOF)
putchar(ch);

fclose(fp);

return 0;
}
</pre>

运行结果：

<blockquote>
[sbso@localhost c]$ gcc fputc_fgetc_test.c -o fputc_fgetc_test
[sbso@localhost c]$ ./fputc_fgetc_test
hello world. www.emacsvi.com
must enter ctrl-d over the input.
ok goodbye.
hello world. www.emacsvi.com
must enter ctrl-d over the input.
ok goodbye.
[sbso@localhost c]$
[sbso@localhost c]$ cat test2
hello world. www.emacsvi.com
must enter ctrl-d over the input.
ok goodbye.
[sbso@localhost c]$
</blockqoute>