malloc () test

This is a discussion on malloc () test within the C Programming forums, part of the General Programming Boards category; I am new to c how can I test that malloc() has successfully giving 26 bytes of memory example t=(char*)malloc(26 ...

  1. #1
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    Question malloc () test

    I am new to c

    how can I test that malloc() has successfully giving 26 bytes of memory

    example t=(char*)malloc(26 * sizeof(char));

    how can i test this function

    thanks

  2. #2
    Code Goddess Prelude's Avatar
    Join Date
    Sep 2001
    Posts
    9,796
    If malloc fails then it will return a NULL pointer, otherwise you got your memory:
    Code:
    var = malloc ( 26 * sizeof ( char ) );
    if ( var != NULL ) {
      /* It's good, work with it. */
    }
    else {
      /* Bad, handle the error */
    }
    And please don't cast malloc, it's not needed and can hide other problems.

    -Prelude
    My best code is written with the delete key.

  3. #3
    End Of Line Hammer's Avatar
    Join Date
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    Posts
    6,231
    You make sure that it's return value is not NULL. If it is, it failed.
    Code:
    if ((ptr = malloc(26)) == NULL)
    {
    	printf("memory problem!");
    	return 1;
    }
    When all else fails, read the instructions.
    If you're posting code, use code tags: [code] /* insert code here */ [/code]

  4. #4
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    Thumbs up

    Thank you all for the help

    But is there a way to print how much memory was assigned?

  5. #5
    Code Goddess Prelude's Avatar
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    >But is there a way to print how much memory was assigned?
    You can't be sure exactly how much malloc gave you since it can and often does give you slightly more than you ask for and sizeof won't work with dynamic memory. So maintain a size variable which holds the size you gave malloc and use that.

    -Prelude
    My best code is written with the delete key.

  6. #6
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    thanks

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