-qinitauto

Purpose

Initializes uninitialized automatic variables to a specific value, for debugging purposes.

Syntax


        .-noinitauto-------------.   
>>- -q--+-initauto--=--hex_value-+-----------------------------><

Defaults

-qnoinitauto

Parameters

hex_value: A one- to eight-digit hexadecimal number.

To initialize each byte of storage to a specific value, specify one or two digits for the hex_value.
To initialize each word of storage to a specific value, specify three to eight digits for the hex_value.
In the case where less than the maximum number of digits are specified for the size of the initializer requested, leading zeros are assumed.
In the case of word initialization, if an automatic variable is smaller than a multiple of 4 bytes in length, the hex_value is truncated on the left to fit. For example, if an automatic variable is only 1 byte and you specify five digits for the hex_value, the compiler truncates the three digits on the left and assigns the other two digits on the right to the variable. See Example 1.
If an automatic variable is larger than the hex_value in length, the compiler repeats the hex_value and assigns it to the variable. See Example 1.
If the automatic variable is an array, the hex_value is copied into the memory location of the array in a repeating pattern, beginning at the first memory location of the array. See Example 2.
You can specify alphabetic digits as either uppercase or lowercase.
The hex_value can be optionally prefixed with 0x, in which x is case-insensitive.

Usage

The -qinitauto option provides the following benefits:

Setting hex_value to zero ensures that all automatic variables that are not explicitly initialized when declared are cleared before they are used.
You can use this option to initialize variables of real or complex type to a signaling or quiet NaN, which helps locate uninitialized variables in your program.

This option generates extra code to initialize the value of automatic variables. It reduces the runtime performance of the program and is to be used for debugging purposes only.

Restrictions:

Objects that are equivalenced, structure components, and array elements are not initialized individually. Instead, the entire storage sequence is initialized collectively.
The -qinitauto=hex_value option does not initialize variable length arrays or memory allocated through the __alloca function.

Predefined macros

__INITAUTO__ is defined to the least significant byte of the hex_value that is specified on the -qinitauto option or pragma; otherwise, it is undefined.
__INITAUTO_W__ is defined to the byte hex_value, repeated four times, or to the word hex_value, which is specified on the -qinitauto option or pragma; otherwise, it is undefined.

For example:

For option -qinitauto=0xABCD, the value of __INITAUTO__ is 0xCDu, and the value of __INITAUTO_W__ is 0x0000ABCDu.
For option -qinitauto=0xCD, the value of __INITAUTO__ is 0xCDu, and the value of __INITAUTO_W__ is 0xCDCDCDCDu.

Examples

Example 1: Use the -qinitauto option to initialize automatic variables of scalar types.

#include <stdio.h>

int main() 
{
  char a;
  short b;
  int c;
  long long int d;

  printf("char a = 0x%X\n",(char)a);
  printf("short b = 0x%X\n",(short)b);
  printf("int c = 0x%X\n",c);
  printf("long long int d = 0x%llX\n",d);
}

If you compile the program with -qinitauto=AABBCCDD, for example, the result is as follows:

char a = 0xDD
short b = 0xFFFFCCDD
int c = 0xAABBCCDD
long long int d = 0xAABBCCDDAABBCCDD

Example 2: Use the -qinitauto option to initialize automatic array variables.

#include <stdio.h>
#define ARRAY_SIZE 5

int main() 
{
  char a[5];
  short b[5];
  int c[5];
  long long int d[5];
  
  printf("array of char: ");
  for (int i = 0; i<ARRAY_SIZE; i++)
    printf("0x%1X ",(unsigned)a[i]);
  printf("\n");

  printf("array of short: ");
  for (int i = 0; i<ARRAY_SIZE; i++)
    printf("0x%1X ",(unsigned)b[i]);
  printf("\n");

  printf("array of int: ");
  for (int i = 0; i<ARRAY_SIZE; i++)
    printf("0x%1X ",(unsigned)c[i]);
  printf("\n");

  printf("array of long long int: ");
  for (int i = 0; i<ARRAY_SIZE; i++)
    printf("0x%1X ",(unsigned)d[i]);
  printf("\n");
}