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yassin.elhakoun
cours_prog
Commits
929c280f
Commit
929c280f
authored
2 years ago
by
Pierre Kunzli
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correction de coquilles
parent
7e8c1280
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slides/allocation_dynamique.md
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929c280f
...
...
@@ -25,7 +25,7 @@ date: "2022-11-22"
frac->denom = -1;
```
-
La zone mémoire
**n'est pas**
initialisée.
-
Désallouer la mémoire explicitement
$
\R
ightarrow$
**fuites mémoires**
.
-
Désallouer la mémoire explicitement
, sinon
**fuites mémoires**
.
-
Il faut connaître la
**taille**
des données à allouer.

{width=100%}
...
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@@ -64,8 +64,8 @@ date: "2022-11-22"
```
C
int *p = malloc(50 * sizeof(int));
// initialize somehow
double
a = p[7];
double
b = *(p + 7); // on avance de 7 "
double
"
int
a = p[7];
int
b = *(p + 7); // on avance de 7 "
int
"
p[0] == *p; // le pointeur est le premier élément
```
...
...
@@ -96,7 +96,7 @@ $$
```
-
En effet, un pointeur est aussi une variable (une variable qui contient une adresse mémoire).
-
Chaque
`*`
{.C}
ou
`&`
{.C}
rajoute une indirection.
-
Chaque
`*`
{.C} rajoute une indirection.
# Allocation dynamique de mémoire (6/7)
...
...
@@ -145,14 +145,14 @@ void initialize_to(int32_t *p, size_t size, int32_t val) {
```
C
// alloue un tableau de taille 50 et l'initialise à -1
int32_t *p = initialize_to(
p,
50, -1);
int32_t *p = initialize_to(50, -1);
free(p); // ne pas oublier
```
. . .
```
C
uint32_t initialize_to(
int32_t *p,
size_t size, int32_t val) {
uint32_t initialize_to(size_t size, int32_t val) {
int32_t *p = malloc(size * sizeof(*p));
for (size_t i = 0; i < size; ++i) {
p[i] = val;
...
...
@@ -222,20 +222,6 @@ p[20] = 1.3;
*
Mais il ne peut contenir que
`50 / 4`
floats (un float est composé de 32 bits).
*
On dépasse la capacité de la mémoire allouée: comportement indéfini.
# Questions
## Que fait le code suivant?
```
C
float *p = malloc(50);
p[20] = 1.3;
```
. . .
*
On déclare un pointeur de floats de taille 50 octets.
*
Mais il ne peut contenir que
`50 / 4`
floats (un float est composé de 32 bits).
*
On dépasse la capacité de la mémoire alloué: comportement indéfini.
# Questions
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