Note for fopen and note for fopen

Source: Internet
Author: User
Tags microsoft c

Note for fopen and note for fopen

Organized from https://msdn.microsoft.com/zh-cn/library/t3ayayh1 (VS.80). aspx

Errno, _ doserrno, _ sys_errlist, and _ sys_nerr

 

These global variables include the error code used by the perror and strerror functions to print error messages. Use the more secure feature versions listed in the following table to replace their global variables.

Global Variable Functional Equivalents

_ Doserrno

_ Get_doserrno, _ set_doserrno

_ Errno

_ Get_errno, _ set_errno

These variables are declared in STDLIB. H

extern int _doserrno; extern int errno; extern char *_sys_errlist[ ];extern int _sys_nerr;
Remarks

Errno is set for errors in system-level calls. Because errno retains the value set for its last call, this value may be changed by subsequent calls. Always check errno before and after possible calls.
In the error, errno is not necessarily set to the same value as the error code returned by the system call. For I/O operations, use _ doserrno to access the operating system error code of errno code. For most non-I/O operations, the value of _ doserrno is undefined.
Each error value is associated with an error message that can be printed using perror or stored in a string using strerror. Perror and strerror use the _ sys_errlist array and _ sys_nerr (number of elements in _ sys_errlist) to process error information.
The library mathematical routine sets errno by calling _ matherr. To handle mathematical errors, write your own routine according to the _ matherr reference description and name it _ matherr.
All ERRNO values defined as pre-defined constants in errno. H are UNIX compatible and listed below. Only ERANGE, EILSEQ, And EDOM are specified in the ANSI standard.

Constant System error message Value

EPERM

Operation not permitted

1

ENOENT

No such file or directory

2

ESRCH

No such process

3

EINTR

Interrupted function

4

EIO

I/O error

5

ENXIO

No such device or address

6

E2BIG

Argument list too long

7

ENOEXEC

Exec format error

8

EBADF

Bad file number

9

ECHILD

No spawned processes

10

EAGAIN

No more processes or not enough memory or maximum nesting level reached

11

ENOMEM

Not enough memory

12

EACCES

Permission denied

13

EFAULT

Bad address

14

EBUSY

Device or resource busy

16

EEXIST

File exists

17

EXDEV

Cross-device link

18

ENODEV

No such device

19

ENOTDIR

Not a directory

20

EISDIR

Is a directory

21

EINVAL

Invalid argument

22

ENFILE

Too program files open in system

23

EMFILE

Too program open files

24

ENOTTY

Inappropriate I/O control operation

25

EFBIG

File too large

27

ENOSPC

No space left on device

28

ESPIPE

Invalid seek

29

EROFS

Read-only file system

30

EMLINK

Too many links

31

EPIPE

Broken pipe

32

EDOM

Math argument

33

ERANGE

Result too large

34

EDEADLK

Resource deadlock wocould occur

36

EDEADLOCK

Same as EDEADLK for compatibility with older Microsoft C versions

36

ENAMETOOLONG

Filename too long

38

ENOLCK

No locks available

39

ENOSYS

Function not supported

40

ENOTEMPTY

Directory not empty

41

EILSEQ

Illegal byte sequence

42

STRUNCATE

String was truncated

80

Note: fopen has a trap. Of course, it is only for beginners.

The fopen method is defined as follows:

FILE*fopen(const char * __restrict __filename, const char * __restrict __mode) __DARWIN_ALIAS_STARTING(__MAC_10_6, __IPHONE_2_0, __DARWIN_ALIAS(fopen));

Fopen has two parameters: one is the file name _ filename you want to operate, and the other is the operation _ mode you want to perform. There is nothing to say about the mode. The filename parameter, if you only upload the file name you want to operate, and your file is local, you may be prompted that the file cannot be found due to Path Problems. Error = 2 (No such file or directory) There is No relevant path or this file does not exist.

In this case, there are two solutions:

One is to use w's mode locally to create a file. to operate on this file, you can ensure that the file is in your current directory, but this is not necessarily applicable, for example, I want to read a bind file of a font, and then convert the Unicode font matrix in the font file into utf8, store it in an array, and write it into the file.

The second method is relatively simple. You can try the absolute path, find the absolute path of the file, and set the parameter _ filename to OK. Note that, paths generally contain "\" characters, which are translated in C/C ++;

All escape characters and their meanings:
Escape characters Meaning ASCII value (decimal)
\ Bell (BEL) 007
\ B Return to BS to move the current position to the previous column. 008
\ F Change page (FF), move the current position to the beginning of the next page 012
\ N Line feed (LF), move the current position to the beginning of the next line 010
\ R Press enter (CR) to move the current position to the beginning of the line 013
\ T Horizontal tabulation (HT) (jump to the next TAB) 009
\ V Vertical tabulation (VT) 011
\\ Represents a backslash character ''\' 092
\' Represents a single quotation mark (apostrophes) character 039
\" Represents a double quotation mark character 034
\?
  
Represents a question mark
  
063
  
\ 0 NULL) 000
\ Ooo Any character from 1 to 3 octal digits Three octal nodes
\ Xhh Any character in hexadecimal notation between 1 and 2 Two hexadecimal
  Note: Yes. slashes: "/" and backslash: "\" are not interchangeable here.Therefore, if your path is c: \ demo \ abc.txt, You need to input the parameter _ filename = c: \ demo \ abc.txt
 1 #include <iostream> 2 #include <fstream> 3  4 int main () 5 { 6     std::cout << "hello world \n"; 7      8     FILE *fp; 9     char *ch = "";10     char buff[100];11 12     errno_t err = fopen_s(&fp,"c:\\Users\\zhi\\Desktop\\abc.txt","r");13 14     if(err == 0)15     {16         printf("the file open successful!");17         18         ch = fgets(buff,100,fp);19         printf("ch is :%s",ch);20         fclose(fp);21 22     }else{23         printf("err:%d",err);24         printf("the file open not OK!");25     }26     return 0;27 }

These are all problems encountered yesterday, but they have grown up.

 

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