如何确定在读取所有字母之前fgets是否停止? [英] How to determine if fgets stopped before all letters were read?

问题描述

我做这样的事情:

char buf[100];              
int n = 0;                  
char save[100][100];        

while (fgets(buf,100, file)!=NULL) {
    strcpy(save[n], buf);
    printf("%s",buf);
    n++;
}

我以前用错误处理打开了FILE = *file. 我只想读取少于或等于100个字符的行.那些具有更多字符的字符，我想忽略并将一些特殊消息写入保存"数组或perror或stout流.

I opened a FILE = *file with error handling before. I only want to read the lines that have less than or equal to 100 characters. Those that feature more characters, I want to ignore and write some special message to the "save" array or to the perror or stout stream.

但是，我怎么可能知道我刚好是100个字符还是我的fgets只是停止阅读而已?

However, how can I possibly know whether I got exactly 100 characters or my fgets has simply stopped reading at its limit?

我怎么知道我是否一开始就获得了100多张?

How can I know whether I got more than 100 in the first place?

推荐答案

首先让我们假设fgets()不会读取空字符.如果是这样，则以下方法可能不够用.

First let us assume that fgets() is not going to read a null character. If it does, the following method may be insufficient.

我只想读取少于或等于100个字符的行.那些功能更多的字符，我想忽略，并向保存"数组中写入一些特殊消息

I only want to read the lines that have less than or equal to 100 characters. Those that feature more characters, I want to ignore and write some special message to the "save" array

问题1. '\n'或 Enter 是 100个字符的一部分吗?让我们假设事实并非如此.

Problem 1. Is the '\n' or Enter part of the 100 characters? Let us assume it is not.

OP似乎仍然想读取该行，无论该行长于或短于100个字符或COLS个字符，那么这只是一个如何处理它的问题.

OP appears to still want to read the line, be it longer or shorter than 100 or COLS characters, it is just a question of what to do with it then.

推荐COLS+3的缓冲区.一个用于空字符，一个用于'\n'，一个用于超长行检测.

Recommend a buffer of COLS+3. One for the null character, one for the '\n' and one for extra long line detection.

#define ROWS 100
#define COLS 100
char save[ROWS][COLS+1];  // +1 for \0      
char buf[COLS + 3];              
int n = 0;                  

while (n < ROWS && fgets(buf, sizeof buf, file)!=NULL) {
  size_t len = strlen(buf);
  bool EOLorEOFfound = false;

  // lop off potential \n
  if (len > 0 && buf[len - 1] == '\n') {
    buf[--len] = '\0';
    EOLorEOFfound = true;
  }

  // if line is too long ...
  if (len > COLS) {
    // consume rest of line
    while (!EOLorEOFfound) {
      int ch = fgetc(file);
      EOLorEOFfound = ch == '\n' || ch == EOF;
    }
    // write some special message to the "save" array
    assert(COLS >= 3);
    strcpy(save[n], "***");
  } 
  // Line not too long
  else {
    strcpy(save[n], buf);  // or memcpy(save[n], buf, len+1);
    printf("%s\n", buf);
  }
  n++;
}

这篇关于如何确定在读取所有字母之前fgets是否停止?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！