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Home php教程 PHP源碼 一起學習用PHP讀取文件的正確方法

一起學習用PHP讀取文件的正確方法

Jun 08, 2016 pm 05:32 PM
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今天做讀取文件練習的時候遇到一個問題,遂在百度上尋找相關解決方法.發(fā)現(xiàn)此篇文章,自我感覺良好,特轉載過來,供大家參考,相信大家會有不一樣的收獲..

??? fopen 方法可能是以前的 C 和 C++ 程序員最熟悉的,因為如果您使用過這些語言,那么它們或多或少都是您已掌握多年的工具。對于這些方法中的任何一種,通過使用 fopen(用于讀取數(shù)據(jù)的函數(shù))的標準方法打開文件,然后使用 fclose 關閉文件,如清單 1 所示。

??? 清單1:用fgets打開并讀取文件

$file_handle = fopen("myfile", "r");

while (!feof($file_handle)) {

$line = fgets($file_handle);

echo $line;

}

fclose($file_handle);

??? 雖然大多數(shù)具有多年編程經(jīng)驗的程序員都熟悉這些函數(shù),但是讓我對這些函數(shù)進行分解。有效地執(zhí)行以下步驟:

??? 1、打開文件。$file_handle 存儲了一個對文件本身的引用。

??? 2、檢查您是否已到達文件的末尾。

??? 3、繼續(xù)讀取文件,直至到達文件末尾,邊讀取邊打印每行。

??? 4、關閉文件。

??? 記住這些步驟,我將回顧在這里使用的每個文件函數(shù)。

??? fopen

??? fopen 函數(shù)將創(chuàng)建與文件的連接。我之所以說“創(chuàng)建連接”,是因為除了打開文件之外,fopen 還可以打開一個 URL:

$fh = fopen("http://127.0.0.1/", "r");

??? 這行代碼將創(chuàng)建一個與以上頁面的連接,并允許您開始像讀取一個本地文件一樣讀取它。

??? 注: fopen 中使用的 “r” 將指示文件以只讀方式打開。由于將數(shù)據(jù)寫入文件不在本文的討論范圍內,因此我將不列出所有其他選項。但是,如果是從二進制文件讀取以獲得跨平臺兼容性,則應當將 “r” 更改為 “rb”。稍后您將看到這樣的示例。

??? feof

??? feof 命令將檢測您是否已經(jīng)讀到文件的末尾并返回 True 或 False。清單 1 中的循環(huán)將繼續(xù)執(zhí)行,直至您達到文件“myfile”的末尾。注:如果讀取的是 URL 并且套接字由于不再有任何數(shù)據(jù)可以讀取而超時,則 feof 也將返回 False。

??? fclose

??? 向前跳至清單 1 的末尾,fclose 將實現(xiàn)與 fopen 相反的功能:它將關閉指向文件或 URL 的連接。執(zhí)行此函數(shù)后,您將不再能夠從文件或套接字中讀取任何信息。

??? fgets

??? 在清單 1 中回跳幾行,您就到達了文件處理的核心:實際讀取文件。fgets 函數(shù)是處理第一個示例的首選武器。它將從文件中提取一行數(shù)據(jù)并將其作為字符串返回。在那之后,您可以打印或者以別的方式處理數(shù)據(jù)。清單 1 中的示例將精細地打印整個文件。

??? 如果決定限制處理數(shù)據(jù)塊的大小,您可以將一個參數(shù)添加到 fgets 中限制最大行長度。例如,使用以下代碼將行長度限制為 80 個字符:

$string = fgets($file_handle, 81);

??? 回想 C 中的“”字符串末尾終止符,將長度設為比實際所需值大一的數(shù)字。因而,如果需要 80 個字符,則以上示例使用 81。應養(yǎng)成以下習慣:只要對此函數(shù)使用行限制,就添加該額外字符。

??? fread

??? fgets 函數(shù)是多個文件讀取函數(shù)中惟一一個可用的。它是一個更常用的函數(shù),因為逐行解析通常會有意義。事實上,幾個其他函數(shù)也可以提供類似功能。但是,您并非總是需要逐行解析。

??? 這時就需要使用 fread。
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