* exit()函数关闭所有打开的文件并终止程序。exit()函数的参数会被传递给一些操作系统，包括UNIX、Linux和MS DOS，以供其他程序使用。通常的约定是正常终止的程序传递值0，非正常终止的程序传递非0值。
ANSI C标准规定使用宏EXIT_SUCCESS来指示程序成功终止，使用宏EXIT_FAILURE来指示程序非成功终止。
return 和 exit() 的一个区别在于，即使在除main()之外的函数中调用exit()，它也将终止程序。
* w/w+ 首先将文件长度截为0
rb+ wb ab ab+ a+b wb+ w+b 类似，只是使用二进制模式而非文本模式打开文件
* ch=getc(fp);//从指针fp指定的文件中获取一个字符
putc(ch,fpout);//将字符写入fpout指针指定的文件中
* 文件结尾 getc(fp)==EOF
/* addaword.c -- uses fprintf(), fscanf(), and rewind() */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAX 41
int main(void)
{
FILE *fp;
char words[MAX];
if ((fp = fopen("wordy", "a+")) == NULL)
{
fprintf(stdout,"Can't open \"wordy\" file.\n");
exit(EXIT_FAILURE);
}
puts("Enter words to add to the file; press the #");
puts("key at the beginning of a line to terminate.");
while ((fscanf(stdin,"%40s", words) == 1) && (words[0] != '#'))
fprintf(fp, "%s\n", words);
puts("File contents:");
rewind(fp); /* go back to beginning of file */
while (fscanf(fp,"%s",words) == 1)
puts(words);
puts("Done!");
if (fclose(fp) != 0)
fprintf(stderr,"Error closing file\n");
return 0;
}
// reducto.c -- reduces your files by two-thirds!
#include <stdio.h>
#include <stdlib.h> // for exit()
#include <string.h> // for strcpy(), strcat()
#define LEN 40
int main(int argc, char *argv[])
{
FILE *in, *out; // declare two FILE pointers
int ch;
char name[LEN]; // storage for output filename
int count = 0;
// check for command-line arguments
if (argc < 2)
{
fprintf(stderr, "Usage: %s filename\n", argv[0]);
exit(EXIT_FAILURE);
}
// set up input
if ((in = fopen(argv[1], "r")) == NULL)
{
fprintf(stderr, "I couldn't open the file \"%s\"\n",
argv[1]);
exit(EXIT_FAILURE);
}
// set up output
strncpy(name,argv[1], LEN - 5); // copy filename
name[LEN - 5] = '\0';
strcat(name,".red"); // append .red
if ((out = fopen(name, "w")) == NULL)
{ // open file for writing
fprintf(stderr,"Can't create output file.\n");
exit(3);
}
// copy data
while ((ch = getc(in)) != EOF)
if (count++ % 3 == 0)
putc(ch, out); // print every 3rd char
// clean up
if (fclose(in) != 0 || fclose(out) != 0)
fprintf(stderr,"Error in closing files\n");
return 0;
}
* fprint()和fscanf()与printf()和scanf()区别不大，关键在于前两个需要第一个参数来指定合适的文件
* fgets()和gets()不一样 他有三个参数 第一个和gets()一样 都是存储输入的地址
fgets(buf, MAX, fp) fgets()函数读取到它所遇到的第一个换行字符的后面，或者读取比字符串的最大长度MAX少一个的字符，
或者读取到文件结尾，然后fgets()函数向末尾添加一个空字符以构成一个字符串。所以，字符串的最大长度代表字符的最大数目再加上一个空字符
如果fgets()函数在达到字符最大数目之前读完了一整行，他将在字符串的空字符之前添加一个换行符以标记一行结束
而gets()读取换行符后将其丢弃，fets()函数可以防止存储溢出
与gets()类似，fgets()遇到EOF会返回NULL
fputs()两个参数，依次是一个字符串的地址和和一个文件指针 与puts()不同，fputs()函数打印时不添加换行符
/* reverse.c -- displays a file in reverse order */
#include <stdio.h>
#include <stdlib.h>
#define CNTL_Z '\032' /* eof marker in DOS text files */
#define SLEN 81
int main(void)
{
char file[SLEN];
char ch;
FILE *fp;
long count, last;
puts("Enter the name of the file to be processed:");
scanf("%80s", file);
if ((fp = fopen(file,"rb")) == NULL)
{ /* read-only mode */
printf("reverse can't open %s\n", file);
exit(EXIT_FAILURE);
}
fseek(fp, 0L, SEEK_END); /* go to end of file */
last = ftell(fp);
for (count = 1L; count <= last; count++)
{
fseek(fp, -count, SEEK_END); /* go backward */
ch = getc(fp);
if (ch != CNTL_Z && ch != '\r') /* MS-DOS files */
putchar(ch);
}
putchar('\n');
fclose(fp);
return 0;
}
* fseek()第一个参数为FILE指针，第二个为偏移量，第三个为模式(SEEK_SET 文件开始处；SEEK_CUR 文件当前处；SEEK_END 文件结尾处)
偏移量 0L 10L 2L -10L
ftell为long类型 返回文件的当前位置 ftell(fp)
* size_t fwrite(const void * restrict ptr, size_t size, size_t nmemb, FILE * restrict fp) 将二进制数据写入文件
ptr--数据块地址 size--数据块大小(以字节为单位) nmemb--数据块的数目 fp--要写入的文件
size_t fread(const void * restrict ptr, size_t size, size_t nmemb, FILE * restrict fp) 读取通过fwrite()写入的文件数据
ptr--读入文件数据的内存存储地址 fp--要写入的文件
double earnings[10];
fread(earnings, sizeof(double), 10, fp);//该调用将10个double值复制到earnings数组中
* 把多个文件的内容追加到一个文件中
/* append.c -- appends files to a file */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define BUFSIZE 4096
#define SLEN 81
void append(FILE *source, FILE *dest);
char * s_gets(char * st, int n);
int main(void)
{
FILE *fa, *fs; // fa for append file, fs for source file
int files = 0; // number of files appended
char file_app[SLEN]; // name of append file
char file_src[SLEN]; // name of source file
int ch;
puts("Enter name of destination file:");
s_gets(file_app, SLEN);
if ((fa = fopen(file_app, "a+")) == NULL)
{
fprintf(stderr, "Can't open %s\n", file_app);
exit(EXIT_FAILURE);
}
if (setvbuf(fa, NULL, _IOFBF, BUFSIZE) != 0)
{
fputs("Can't create output buffer\n", stderr);
exit(EXIT_FAILURE);
}
puts("Enter name of first source file (empty line to quit):");
while (s_gets(file_src, SLEN) && file_src[0] != '\0')
{
if (strcmp(file_src, file_app) == 0)
fputs("Can't append file to itself\n",stderr);
else if ((fs = fopen(file_src, "r")) == NULL)
fprintf(stderr, "Can't open %s\n", file_src);
else
{
if (setvbuf(fs, NULL, _IOFBF, BUFSIZE) != 0)
{
fputs("Can't create input buffer\n",stderr);
continue;
}
append(fs, fa);
if (ferror(fs) != 0)
fprintf(stderr,"Error in reading file %s.\n",
file_src);
if (ferror(fa) != 0)
fprintf(stderr,"Error in writing file %s.\n",
file_app);
fclose(fs);
files++;
printf("File %s appended.\n", file_src);
puts("Next file (empty line to quit):");
}
}
printf("Done appending. %d files appended.\n", files);
rewind(fa);
printf("%s contents:\n", file_app);
while ((ch = getc(fa)) != EOF)
putchar(ch);
puts("Done displaying.");
fclose(fa);
return 0;
}
void append(FILE *source, FILE *dest)
{
size_t bytes;
static char temp[BUFSIZE]; // allocate once
while ((bytes = fread(temp,sizeof(char),BUFSIZE,source)) > 0)
fwrite(temp, sizeof (char), bytes, dest);
}
char * s_gets(char * st, int n)
{
char * ret_val;
char * find;
ret_val = fgets(st, n, stdin);
if (ret_val)
{
find = strchr(st, '\n'); // look for newline
if (find) // if the address is not NULL,
*find = '\0'; // place a null character there
else
while (getchar() != '\n')
continue;
}
return ret_val;
}
* 使用二进制I/O进行随机存取
/* randbin.c -- random access, binary i/o */
#include <stdio.h>
#include <stdlib.h>
#define ARSIZE 1000
int main()
{
double numbers[ARSIZE];
double value;
const char * file = "numbers.dat";
int i;
long pos;
FILE *iofile;
// create a set of double values
for(i = 0; i < ARSIZE; i++)
numbers[i] = 100.0 * i + 1.0 / (i + 1);
// attempt to open file
if ((iofile = fopen(file, "wb")) == NULL)
{
fprintf(stderr, "Could not open %s for output.\n", file);
exit(EXIT_FAILURE);
}
// write array in binary format to file
fwrite(numbers, sizeof (double), ARSIZE, iofile);
fclose(iofile);
if ((iofile = fopen(file, "rb")) == NULL)
{
fprintf(stderr,
"Could not open %s for random access.\n", file);
exit(EXIT_FAILURE);
}
// read selected items from file
printf("Enter an index in the range 0-%d.\n", ARSIZE - 1);
while (scanf("%d", &i) == 1 && i >= 0 && i < ARSIZE)
{
pos = (long) i * sizeof(double); // calculate offset
fseek(iofile, pos, SEEK_SET); // go there
fread(&value, sizeof (double), 1, iofile);
printf("The value there is %f.\n", value);
printf("Next index (out of range to quit):\n");
}
// finish up
fclose(iofile);
puts("Bye!");
return 0;
}
