-fmacro-use-commandline

Description

Macros in the command line are preferentially used.

Usage

Add the compilation option -fmacro-use-commandline, and append the -D macro definition to it. For example, -fmacro-use-commandline -DTEST_MACRO=222 defines the DTEST_MACRO macro as 222.

Result

The test case is as follows:

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#define TEST_MACRO 10
 
int main()
{
    printf("Hello World, TEST_MACRO:%d\n", TEST_MACRO);
    return 0;
}

Test command:

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gcc -E test.c -o test.i -fmacro-use-commandline -DTEST_MACRO=222

Figure 1 Option disabled

Figure 2 Option enabled

After the option is enabled, the macro definition in the command line is preferentially used, defining the TEST_MACRO macro as 222.