In C language, the presence or absence of printf sometimes results in segmentation fault.

printf() also uses memory for processing.Therefore, printf() changes the memory content that printf() has used up.

The correct program will not be affected because it does not access the memory that has been used. Incorrect programs can be affected by accessing used memory.

Perhaps your program is accessing memory that printf() has used up.
- If not called: Memory value happens to be segmentation fault
- Called: Memory value does not happen to be segmentation fault
It's just that

• The pointer variable is being handled incorrectly and accessing strange places
• Forgot to initialize automatic variables, and the values that happen to be included are different

is often the cause.

Example of the latter

#include<stdio.h>
void testfunc(void){
    intuninit_auto;
    printf("%d\n", unity_auto);
}
int main() {
    printf("Hello World\n");// Commenting this line changes behavior
    testfunc();
}

In this example, unit_auto is an automatic variable, but it has not been initialized.Therefore, the initial value is indefinite.The indefinite value depends on whether main() internally printf().Example hppa 2.0w-hp-hpux 11.11-gcc-9.2.0 Results

 Without $gccunit.c#printf
$ ./a.out
0
$ With gccuninit2.c#printf
$ ./a.out
Hello World
2046468114
$

In this example, int does not cause errors, but char*unit_auto; does not cause segmentation faults depending on the value.

#You may need to disable the debug assistance features of the compiler when you test it yourself

I can't understand why this happens without reading the generated machine language, but I'll skip it

Don't get me wrong, just because you don't get an error doesn't mean that the memory access violation is gone.
In C language, error checking that takes a long time to execute is omitted, and the error that occurs during execution is just something that happens to be detected by the abnormal behavior.
Most errors are not shown in the table.

Therefore, the behavior is simply that the printf instruction is placed so that the memory placement changes to Bimyo and is no longer detected as an error.
Again, no errors do not mean that the program bug is gone.