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Asked: 2026-05-11T20:53:14+00:00

In GCC, certain warnings require optimization to be enabled. For example: int foo() {

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In GCC, certain warnings require optimization to be enabled. For example:

int foo() {
    int x;
    return x;
}

In order to detect the uninitialized variable, -O must be passed.

$ gcc -W -Wall -c test.c
$ gcc -W -Wall -c test.c -O

test.c: In function ‘foo’:
test.c:3: warning: ‘x’ is used uninitialized in this function

However, this can interfere with debugging. Is there a way to enable just the analysis phases needed for warnings (and not just this particular warning, but as many as possible), without affecting the generated code too much?

I’m using GCC version 4.3.3 (Ubuntu 4.3.3-5ubuntu4) on x86-64.

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1 Answer

  1. Editorial Team

    Try using -Wall instead of -W. -W is deprecated IIRC. (As Jonathan Leffler points out in a comment, -W‘s replacement is -Wextra, not -Wall.)

    -Wunused-variable
    Warn whenever a local variable or non-constant static variable is unused aside from its declaration. This warning is enabled by -Wall.

    3.8 Options to Request or Suppress Warnings

    This behavior has changed in GCC 4.4:

    Uninitialized warnings do not require enabling optimization anymore, that is, -Wuninitialized can be used together with -O0. Nonetheless, the warnings given by -Wuninitialized will probably be more accurate if optimization is enabled.

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