232 lines
5.8 KiB
Markdown
232 lines
5.8 KiB
Markdown
---
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title: Storage
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TARGET DECK: Obsidian::STEM
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FILE TAGS: c17::storage
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tags:
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- c17
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---
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## Dynamic Allocation
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The `<stdlib.h>` header provides the two most prominent functions used for managing dynamic memory: `malloc` and `free`. The former is used to allocate new memory whereas the latter is used to annihilate it.
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```c
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void* malloc(size_t size);
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void free(void*);
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```
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%%ANKI
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Basic
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Which standard library header exposes `malloc`?
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Back: `<stdlib.h>`
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1732755874715-->
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END%%
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%%ANKI
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Basic
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Which standard library header exposes `free`?
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Back: `<stdlib.h>`
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1732755874716-->
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END%%
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%%ANKI
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Basic
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Why is `malloc` named the way it is?
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Back: It stands for **m**emory **alloc**ate.
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1732755874717-->
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END%%
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%%ANKI
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Basic
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What two functions are most prominently used for dynamic allocation?
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Back: `malloc` and `free`.
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1732755874718-->
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END%%
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%%ANKI
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Cloze
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Generally speaking, memory created with {`malloc`} should be deleted with {`free`}.
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1732755874719-->
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END%%
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%%ANKI
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Basic
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What three specialized variants of `malloc` are exposed by `<stdlib.h>`?
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Back: `calloc`, `realloc`, and `aligned_alloc`.
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1732755874720-->
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END%%
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%%ANKI
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Basic
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On success, what does a call to `malloc` return?
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Back: A `void*` pointer.
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1732755874721-->
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END%%
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%%ANKI
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Basic
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On failure, what does a call to `malloc` return?
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Back: A null pointer value.
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1732755874722-->
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END%%
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%%ANKI
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Basic
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What are the argument(s) to `malloc`?
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Back: The size (in bytes) of the block of memory to allocate.
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1732755874723-->
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END%%
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%%ANKI
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Basic
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What is wrong with the following code snippet?
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```c
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double *d = (double*)malloc(sizeof *d);
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```
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Back: The return type of `malloc` should not be cast.
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1732755874724-->
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END%%
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%%ANKI
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Basic
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What is wrong with the following code snippet?
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```c
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double *d = malloc(sizeof *d);
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```
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Back: N/A. This is valid.
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1732755874725-->
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END%%
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%%ANKI
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Basic
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What possible error can occur by explicitly casting the return type of `malloc`?
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Back: If `<stdlib.h>` isn't imported, older C compilers assume `malloc` returns an `int`.
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1732755874726-->
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END%%
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%%ANKI
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Basic
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Without `<stdlib.h>`, an older C compiler might assume what `malloc` declaration?
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Back:
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```c
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int malloc();
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```
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1732755874727-->
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END%%
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%%ANKI
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Basic
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Within `<stdlib.h>`, what function prototype does `malloc` have?
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Back:
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```c
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void* malloc(size_t size);
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```
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1732755874728-->
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END%%
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%%ANKI
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Cloze
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Storage allocated through `malloc` is {uninitialized} and has {no type}.
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1732755874729-->
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END%%
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%%ANKI
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Basic
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Does the following invoke undefined behavior? Why or why not?
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```c
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free(0);
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```
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Back: No. `free` ignores null pointer values.
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1732755874730-->
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END%%
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%%ANKI
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Basic
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Does the following invoke undefined behavior? Why or why not?
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```c
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double d = 0.0;
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free(&d);
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```
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Back: Yes. `d` was not dynamically allocated.
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1732755874731-->
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END%%
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%%ANKI
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Basic
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Does the following invoke undefined behavior? Why or why not?
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```c
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double* d = malloc(sizeof *d);
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free(&d);
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```
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Back: Yes. `d` was not dynamically allocated.
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1732755874732-->
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END%%
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%%ANKI
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Basic
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Does the following invoke undefined behavior? Why or why not?
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```c
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double* d = malloc(sizeof *d);
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free(d);
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```
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Back: No. The address `d` pointed to was dynamically allocated.
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1732755874733-->
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END%%
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%%ANKI
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Basic
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Does the following invoke undefined behavior? Why or why not?
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```c
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double* d = malloc(sizeof *d);
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free(d);
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d = 0;
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free(d);
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```
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Back: No. `free` ignores null pointer values.
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1732755874734-->
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END%%
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%%ANKI
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Basic
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Does the following invoke undefined behavior? Why or why not?
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```c
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double* d = malloc(sizeof *d);
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free(d);
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free(d);
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```
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Back: Yes. `free` should not be invoked on already `free`'d data.
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1732755874735-->
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END%%
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%%ANKI
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Basic
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`malloc` and its variants all have the `size` parameter in what position?
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Back: The last position.
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Reference: Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020).
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<!--ID: 1732755874736-->
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END%%
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## Bibliography
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* Jens Gustedt, _Modern C_ (Shelter Island, NY: Manning Publications Co, 2020). |