Eclipse – How to configure GCC in Eclipse to use C99

c99eclipsegcc

I'm working on a small C project in Eclipse; I just installed Eclipse from the Ubuntu Software Center and added C/C++ Language Support. I can build, run, and debug simple C programs fine.

But I'm using some C99 features now, and Eclipse complains, saying "'for' loop initial declarations are only allowed in C99 mode".

I thought you'd set C99 mode for GCC in the makefile, but the makefile is auto-generated by Eclipse so any changes I make would be overwritten, but I don't see anywhere to put GCC compiler options anywhere in Eclipse's preferences nor my Project Properties windows.

So where do I define C99 mode?

Best Answer

Go into project properties. Search for C/C++Build -> Settings. In the Tool Settings tab search for GCC C compiler and then Miscellaneous. In other flags text box add the -std=c99. It should work fine.

Related Solutions

Eclipse – How to you speed up Eclipse

The three most influential factors for Eclipse speed are:

Using the latest version of Eclipse (2020-06 as on 26 June 2020)
Note that David Balažic's comment (July 2014) contradicts that criteria which was working six years ago:

The "same" workspace in Indigo (3.7.2) SR2 loads in 4 seconds, in Kepler SR2 (4.3.2) in 7 seconds and in Luna (4.4.0) in 10 seconds. All are Java EE bundles. Newer versions have more bundled plugins, but still the trend is obvious. (by "same" workspace I mean: same (additionally installed) plugins used, same projects checked out from version control).

Launching it with the latest JDK (Java 14 at the time of writing, which does not prevent you to compile in your Eclipse project with any other JDK you want: 1.4.2, 1.5, 1.6 older...)
```
  -vm jdk1.6.0_10\jre\bin\client\jvm.dll
```
Configuring the eclipse.ini (see this question for a complete eclipse.ini)
```
  -Xms512m
  -Xmx4096m
  [...]
```

The Xmx argument is the amount of memory Eclipse will get (in simple terms). With -Xmx4g, it gets 4 GB of RAM, etc.

Note:

Referring to the jvm.dll has advantages:

Splash screen coming up sooner.
Eclipse.exe in the process list instead of java.exe.
Firewalls: Eclipse wants access to the Internet instead of Java.
Window management branding issues, especially on Windows and Mac.

Dec. 2020, Udo conforms in the comments

From version 4.8 (Photon) an up there was a steady speed gain after each version.
The main platform was optimized every release to load faster, enable more features for the dark theme and to add more features for newer Java versions for the Java development tools.
Especially with-in the last 3 versions the startup time was increased a lot. There should be a significant increase in start-up time with the newest version of Eclipse 2020-12.

In my experience it started a lot faster with each new version.
But: There are still plug-ins which do not follow the new way of using the Eclipse API and are therefore still slow to start.
Since the change to Java 11 as the minimum runtime version starting from Eclipse version 2020-09 at least the core system uses the newer features of the JVM. It is up to the providers of the other plug-ins to upgrade to newer APIs and to use the full power of modern CPUs (e.g. concurrent programming model).

Eclipse – How to change Eclipse to use spaces instead of tabs

Java Editor

Click Window » Preferences
Expand Java » Code Style
Click Formatter
Click the Edit button
Click the Indentation tab
Under General Settings, set Tab policy to: Spaces only
Click OK ad nauseam to apply the changes.

[Note: If necessary save profile with a new name as the default profile cannot be overwritten.]

Default Text Editor

Before version 3.6:

Window->Preferences->Editors->Text Editors->Insert spaces for tabs

Version 3.6 and later:

Click Window » Preferences
Expand General » Editors
Click Text Editors
Check Insert spaces for tabs
Click OK ad nauseam to apply the changes.

Note that the default text editor is used as the basis for many non-Java editors in Eclipse. It's astonishing that this setting wasn't available until 3.3.

C / C++

Click Window » Preferences
Expand C/C++ » Code Style
Click Formatter
Click the New button to create a new profile, then OK to continue
Click the Indentation tab
Under General Settings, set Tab policy to: Spaces only
Click OK ad nauseam to apply the changes.

HTML

Click Window » Preferences
Expand Web » HTML Files
Click Editor
Under Formatting, select the Indent using spaces radio button
Click OK to apply the changes.

CSS

Follow the same instructions for HTML, but select CSS Files instead of HTML Files.

JSP

By default, JSP files follow the formatting preferences for HTML Files.

XML

XML files spacing is configured in Preferences.

Click Window » Preferences
Expand XML » XML Files
Click Editor
Select Indent using spaces
You can specify the Indentation size if needed: number of spaces to indent.