user24065: So I'm trying to create a new file that has underscores in its name. However, when I try this, no file is created.
This works
String fileName = "NMEA.txt";
mySensorData = SD.open(fileName.c_str(), FILE_WRITE); 

This does not work
String fileName = "NMEA__23_33_3__16_7_29.txt";
mySensorData = SD.open(fileName.c_str(), FILE_WRITE); 

Does anyone know why?

user368: 
[The SD library] uses short 8.3 names for files.

source

24065: <p>So I'm trying to create a new file that has underscores in its name. However, when I try this, no file is created.</p>

<p><strong>This works</strong></p>

<pre><code>String fileName = "NMEA.txt";
mySensorData = SD.open(fileName.c_str(), FILE_WRITE); 
</code></pre>

<p><strong>This does not work</strong></p>

<pre><code>String fileName = "NMEA__23_33_3__16_7_29.txt";
mySensorData = SD.open(fileName.c_str(), FILE_WRITE); 
</code></pre>

<p>Does anyone know why?</p>
 368: <blockquote>
  <p>[The SD library] uses short 8.3 names for files.</p>
</blockquote>

<p><a href="https://www.arduino.cc/en/Reference/SD" rel="nofollow">source</a></p>
