CodePudding user response:

CodePudding user response:

//baidu encyclopedia explanation for the fgets function 
//fgtes function prototype is: char * the fgets (char * buf, int bufsize, FILE * stream). 
//from the file structure pointer data read from the stream, each reading a line, read data stored in buf points to an array of characters, 
//most read bufsize - a character at a time (the first bufsize assignment of character '\ 0'), if the file is in the bank, insufficient bufsize characters, 
//read it ends, if the bank (including the final newline), the number of characters than bufsize - 1 is the fgets only returns a 
//incomplete line, but always ends in NULL character buffer, the next call will continue to read the bank of the fgets function returns buf success, 
//fail or read documents ending returns NULL, so we can't directly through the fgets to judge the function return value is wrong and termination, should 
//use feof function or ferror function to judge, 

Reference://https://my.oschina.net/u/3979769/blog/2208662 
//this usage, below is the judgment of the safety file read error or a good way, don't use while (! The feof (fp)), 
//and for the second parameter is the biggest the fgets can read the file number of the characters, generally the largest length is 1024 bytes, 
//while the fgets (... , the stream)) {

/*... */
//} 

//if ferror (stream)) {

/*... */
//} 

//the stream: file pointer, if read keyboard input string, fixed writing for stdin 
//(1) if the keyboard input number of characters less than bufsize - 1, the function will return record, print output is to enter; 
//(2) if the keyboard input of characters is greater than the bufsize - 1, a function go bufsize - 1 characters recorded, the rest of the characters in the data buffer, the next 
//read buffer content directly, will not skip input, such as keyboard input, cause the failure of the input, 

//the return value 
//1. Successful, it returns the first parameter buf. 
//2. When reading characters eof, eof indicator is set, if you haven't read any character encountered this kind of situation, buf to keep the original content, returns NULL. 
//3. If there is a reading error, the error indicator is set, returns NULL, buf value may be changed, 

//how to handle the transfer line operator? 
//traversal string, meet a newline, characters and replace it into empty, empty characters, discarding the input line is the rest of the characters, 

//why do you want to throw away for too long the remaining characters in the input line? 
//the extra character in the input line will be in the buffer, become the input of the next read statements, 

//read the entire line input and empty instead of a newline characters, or read some input, and discard the rest 
Char * s_gets (char * st, int n) 
{
Char * ret_val; 
Int I=0; 
Ret_val=the fgets (st, n, stdin); 
If (ret_val!=NULL) 
{
While (st [I]!='\ n' & amp; & St [I]!='\ 0') 
i++; 

If (st [I]=='\ n') 
St [I]='\ 0'; 
The else 
While (getchar ()! ) 
='\ n'continue; 
} 
Return ret_val; 
}