C语言——IO操作（一）
C语言——IO操作（一）
1 标准IO介绍
I/O: stdio sysio （优先使用标准IO）
IO是一切程序实现的基础。
- stdio
fopen(); fclose(); fgetc(); fputc(); fgets(); fputs(); fread(); fwrite();
scanf(); printf();
fseek(); ftell(); rewind();
fflush();
1.1 fopen() 和 fclose()
- fopen();
FILE *fopen(const char *path, const char *mode);
Upon successful completion. return a FILE pointer. Otherwise, NULL is returned and errno is set to indicate the error.
-----------------------------------
| /usr/include/asm-generic/ |
| error-basse.h errno.h |
-----------------------------------
r Open text file for reading. The stream is positioned at the beginning of
the file.
r+ Open for reading and writing. The stream is positioned at the beginning
of the file.
w Truncate file to zero length or create text file for writing. The stream
is positioned at the beginning of the file.
w+ 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.
a 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.
a+ 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.
- perror() 打印错误原因。
void perror(const char *s);
#include - strerror()
#include - fclose();
int fclose(FILE *stream);
The fclose() function flushes the stream pointed to by stream (writing
any buffered output data using fflush(3)) and closes the underlying file
descriptor.
The behaviour of fclose() is undefined if the stream parameter is an
illegal pointer, or is a descriptor already passed to a previous
invocation of fclose().
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.
打开的文件流一定要关闭！！！
1.2 fgetc() 和 fputc()
- fgetc();
getc 被定义成宏；
fgetc 被定义成函数；
从标准输入流/成功打开的文件流中读入
成功返回 int 失败返回 EOF
- fputc();
同上；
- 简单的copy函数
#include \n" , argv[0]);
exit(-1);
}
fps = fopen(argv[1], "r");
if (fps == NULL){
perror("fopen()");
exit(-1);
}
fpd = fopen(argv[2], "w");
if (fpd == NULL){
fclose(fps);
perror("fopen()");
exit(-1);
}
while (1){
ch = fgetc(fps);
if (ch == EOF){
break;
}
fputc(ch, fpd);
}
fclose(fps);
fclose(fpd);
return 0;
}
使用演示：
--------------------------------------------------------------------
./mycopy /etc/services /tmp/out
- 文件字符统计
#include \n" , argv[0]);
exit(-1);
}
fp = fopen(argv[1], "r");
if (fp == NULL){
perror("fopen()");
exit(-1);
}
while (fgetc(fp) != EOF){
count++;
}
printf("count = %d\n", count);
fclose(fp);
return 0;
}
使用演示：
----------------------------------------------------------------------
./fgetc mycopy.c
结果：
------------------------
count = 714
1.3 fgets() 和 fputs()
- fgets()
gets()函数不安全，不检查缓冲区是否溢出，不要使用gets()。可以用fgets()代替。
char *fgets(char *s, int size, FILE *stream);
reads in at most one less than size characters from stream and stores
them into the buffer pointed to by s. Reading stops after an EOF or a
newline. If a newline is read, it is stored into the buffer. A termi‐
nating null byte ('\0') is stored after the last character in the buffer.
fgets(buf, SIZE, stream); //文件末尾有一个换行符 '\n'
1.读入一个SIZE-1长度的字符串
最后一个字符为'\0' 有效字符为SIZE-1个
2.读入字符串长度小于SIZE
最后为'\n''\0'
- fputs()
char *fputs(const char *s, FILE *stream);
- copy改进
#include \n" , argv[0]);
exit(-1);
}
fps = fopen(argv[1], "r");
if (fps == NULL){
perror("fopen()");
exit(-1);
}
fpd = fopen(argv[2], "w");
if (fpd == NULL){
fclose(fps);
perror("fopen()");
exit(-1);
}
while (fgets(buf, BUF_SIZE, fps) != NULL){
fputs(buf, fpd);
}
fclose(fps);
fclose(fpd);
return 0;
}
1.4 fread() 和 fwrite()
- fread()
size_t fread(void *ptr, size_t size, size_t nmemb, FILE *stream);
size_t fwrite(const void *ptr, size_t size, size_t nmemb, FILE *stream);
PTR_SIZE == size * nmemb;
On success, fread() and fwrite() return the number of items read or
written. This number equals the number of bytes transferred only when
size is 1. If an error occurs, or the end of the file is reached,
the return value is a short item count (or zero).
返回值为成功读取对象的数量，成功至少为1个对象，不足一个对象失败返回0。
- copy改进
while ((n = fread(buf, 1, BUF_SIZE, fps)) > 0){
fwrite(buf, 1, n, fpd);
}