c - 为什么为了使用 fgets 读取多行文本，我们需要设置 fgets()!=NULL？

Question

如果我想使用 fgets 从文本中读取多行，根据我的教科书，我会这样做:

 char str[53];
 ...
 while(fgets(str, max, f)!=NULL){
   ...
 }

如果str只是一行n个字符的字符串，程序如何读取第二行？根据文档，循环到达行尾时不应该停止吗？

fgets Reads characters from stream and stores them as a C string into str until (num-1) characters have been read or either a newline or the end-of-file is reached, whichever happens first.

Answer 1

根据文档:

On success, the function returns str. If the end-of-file is encountered while attempting to read a character, the eof indicator is set (feof). If this happens before any characters could be read, the pointer returned is a null pointer (and the contents of str remain unchanged). If a read error occurs, the error indicator (ferror) is set and a null pointer is also returned (but the contents pointed by str may have changed).

str 是您指定为第一个参数的缓冲区。如果fgets读取完毕，则返回NULL。