blocks|key|1369915|text|文件IO在使用JNI的Android上运行良好。也许你正在尝试打开一个带有错误路径的文件，而没有检查返回代码？我修改了hello-jni示例，以演示确实可以打开文件并向其写入。我希望这能帮到你。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1369916|/*
+*+Copyright+(C)+2009+The+Android+Open+Source+Project
+*
+*+Licensed+under+the+Apache+License,+Version+2.0+(the+"License");
+*+you+may+not+use+this+file+except+in+compliance+with+the+License.
+*+You+may+obtain+a+copy+of+the+License+at
+*
+*++++++http://www.apache.org/licenses/LICENSE-2.0
+*
+*+Unless+required+by+applicable+law+or+agreed+to+in+writing,+software
+*+distributed+under+the+License+is+distributed+on+an+"AS+IS"+BASIS,
+*+WITHOUT+WARRANTIES+OR+CONDITIONS+OF+ANY+KIND,+either+express+or+implied.
+*+See+the+License+for+the+specific+language+governing+permissions+and
+*+limitations+under+the+License.
+*
+*/
#include+<string.h>
#include+<jni.h>
#include+<stdio.h>

/*+This+is+a+trivial+JNI+example+where+we+use+a+native+method
+*+to+return+a+new+VM+String.+See+the+corresponding+Java+source
+*+file+located+at:
+*
+*+++apps/samples/hello-jni/project/src/com/example/HelloJni/HelloJni.java
+*/
jstring
Java_com_example_hellojni_HelloJni_stringFromJNI(+JNIEnv*+env,
++++++++++++++++++++++++++++++++++++++++++++++jobject+thiz+)
{
++++FILE*+file+=+fopen("/sdcard/hello.txt","w%2B");

++++if+(file+!=+NULL)
++++{
++++++++fputs("HELLO+WORLD!\n",+file);
++++++++fflush(file);
++++++++fclose(file);
++++}

++++return+(*env)->NewStringUTF(env,+"Hello+from+JNI+(with+file+io)!");
}|code-block|syntax|javascript|1369917|这是在我的手机上运行后的结果(使用SD卡)：|1369918|$+adb+-d+shell+cat+/sdcard/hello.txt
HELLO+WORLD!|1369919|entityMap^0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|M|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|N|8|@]|9|@]|A|$E|F]]|$1|G|3|H|5|6|7|O|8|@]|9|@]|A|$]]|$1|I|3|J|5|D|7|P|8|@]|9|@]|A|$E|F]]|$1|K|3|-4|5|6|7|Q|8|@]|9|@]|A|$]]]|L|$]]

File IO works fine on Android using JNI. Perhaps you are trying to open a file with a bad path and not checking the return code? I modified the hello-jni example to demonstrate that it is indeed possible to open file and write to it. I hope this helps.

<pre><code>/*
 * Copyright (C) 2009 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 */
#include &lt;string.h&gt;
#include &lt;jni.h&gt;
#include &lt;stdio.h&gt;

/* This is a trivial JNI example where we use a native method
 * to return a new VM String. See the corresponding Java source
 * file located at:
 *
 * apps/samples/hello-jni/project/src/com/example/HelloJni/HelloJni.java
 */
jstring
Java_com_example_hellojni_HelloJni_stringFromJNI( JNIEnv* env,
 jobject thiz )
{
 FILE* file = fopen("/sdcard/hello.txt","w+");

 if (file != NULL)
 {
 fputs("HELLO WORLD!\n", file);
 fflush(file);
 fclose(file);
 }

 return (*env)-&gt;NewStringUTF(env, "Hello from JNI (with file io)!");
}
</code></pre>

Here is the result after running it on my phone (with an SD card):

<pre><code>$ adb -d shell cat /sdcard/hello.txt
HELLO WORLD!
</code></pre>

blocks|key|1154884|text|其他答案是正确的。您可以使用FILE和fopen通过NDK打开文件，但不要忘记为其设置权限。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1154885|在Android清单中：|1154886|<uses-permission+android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>+|code-block|syntax|javascript|1154887|entityMap^0|E|4|J|5|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@$9|P|A|Q|B|C]|$9|R|A|S|B|C]]|D|@]|E|$]]|$1|F|3|G|5|6|7|T|8|@]|D|@]|E|$]]|$1|H|3|I|5|J|7|U|8|@]|D|@]|E|$K|L]]|$1|M|3|-4|5|6|7|V|8|@]|D|@]|E|$]]]|N|$]]

Other answers are correct. You can open a file through the NDK using <code>FILE</code> and <code>fopen</code>, but don't forget to place a permission for it.

In the Android manifest place:

<pre><code>&lt;uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/&gt; 
</code></pre>

blocks|key|1369988|text|确保使用JavaSD卡调用来获取getExternalStorageDirectory()的实际路径，因为较新的设备不会简单地将其映射到"/sdcard“。在这种情况下，尝试使用硬编码位置"/sdcard“将失败。|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1369989|entityMap^0|G|T|0^^$0|@$1|2|3|4|5|6|7|H|8|@$9|I|A|J|B|C]]|D|@]|E|$]]|$1|F|3|-4|5|6|7|K|8|@]|D|@]|E|$]]]|G|$]]

Make sure to use the Java <code>getExternalStorageDirectory()</code> call to get the real path to the sdcard since newer devices don't simply map it to "/sdcard". In that case trying to use a hardcoded location of "/sdcard" will fail.

blocks|key|1370028|text|我想在这里补充我的两点看法，除了设置这个问题的答案中指定的正确权限之外，还要确保授予您的应用程序访问操作系统中存储的权限。权限菜单可以根据手机的不同而不同，一个简单的方法是进入设置菜单，然后搜索“权限”。这将给你一个机会，让你的应用程序从NDK代码访问存储(即sdcard目录)。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|1370029|entityMap^0|0^^$0|@$1|2|3|4|5|6|7|D|8|@]|9|@]|A|$]]|$1|B|3|-4|5|6|7|E|8|@]|9|@]|A|$]]]|C|$]]

I want to add my two cents to the answers here, on top of setting the correct permissions specified in the answer to this question, make sure to give your app permission to access the storage in the OS. The permissions menu could change from phone to phone, an easy way to get to it is by going to the Settings menu and then searching for "Permissions." This will give you a chance to give your app permission to access the storage (ie sdcard directory) from NDK code.

I am using the Android NDK to make an application primarily in C for performance reasons, but it appears that file operations such as fopen do not work correctly in Android. Whenever I try to use these functions, the application crashes. 

How do I create/write to a file with the Android NDK?

File Operations in Android NDK

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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出于性能原因，我主要使用Android NDK来制作一个C语言的应用程序，但似乎文件操作(如fopen )在Android中不能正常工作。每当我尝试使用这些函数时，应用程序都会崩溃。如何使用Android NDK创建/写入文件？

问Android NDK中的文件操作
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