swap_str

Pointers12

Objective

Write a function that exchanges the two char * pointers held at two addresses, without touching a single character of either string.

Steps

a and b are the addresses of two char * variables, so the two strings in play are *a and *b.
Exchange those two pointers: after the call *a holds the pointer that was in *b, and *b holds the pointer that was in *a. One local char * is enough to hold the value being moved.
Copy nothing. The characters of both strings stay exactly where they were, only the two pointers move. No library call is allowed here.
*a or *b may be an empty string or NULL. Move it like any other pointer.
swap_str(&x, &x) is a legal call and must leave x pointing at the string it already pointed at.
When a is NULL or b is NULL, do nothing and return.

examples

$ a = "alpha", b = "beta", swap_str(&a, &b)

a=[beta] b=[alpha]

$ a = "", b = "cargo build --release", swap_str(&a, &b)

a=[cargo build --release] b=[]

$ a points at one[] = "alpha", b points at two[] = "beta", swap_str(&a, &b)

one=[alpha] two=[beta] a=[beta] b=[alpha]

$ a = "git bisect", swap_str(&a, &a)

a=[git bisect]

$ b = "make -j8", swap_str(NULL, &b)

b=[make -j8]

Constraints

Expected files

swap_str.c

Allowed functions

None. Write every helper yourself.

Allowed headers

<stddef.h>defines NULL

Tests

Run the tests to grade your code

Build

01Two ordinary strings

02Lengths far apart

03One character each

04Empty string on the left

05Empty string on the right

06Both strings empty

07Same address on both sides

08Equal contents, the pointers still move

09No character is copied

10A NULL string pointer moves too

11A NULL string pointer moves the other way

12a is NULL, nothing happens

13b is NULL, nothing happens

14Both arguments NULL, no crash

swap_str

Objective

Write a function that exchanges the two char * pointers held at two addresses, without touching a single character of either string.

Steps

a and b are the addresses of two char * variables, so the two strings in play are *a and *b.
Exchange those two pointers: after the call *a holds the pointer that was in *b, and *b holds the pointer that was in *a. One local char * is enough to hold the value being moved.
Copy nothing. The characters of both strings stay exactly where they were, only the two pointers move. No library call is allowed here.
*a or *b may be an empty string or NULL. Move it like any other pointer.
swap_str(&x, &x) is a legal call and must leave x pointing at the string it already pointed at.
When a is NULL or b is NULL, do nothing and return.

examples

$ a = "alpha", b = "beta", swap_str(&a, &b)

a=[beta] b=[alpha]

$ a = "", b = "cargo build --release", swap_str(&a, &b)

a=[cargo build --release] b=[]

$ a points at one[] = "alpha", b points at two[] = "beta", swap_str(&a, &b)

one=[alpha] two=[beta] a=[beta] b=[alpha]

$ a = "git bisect", swap_str(&a, &a)

a=[git bisect]

$ b = "make -j8", swap_str(NULL, &b)

b=[make -j8]

Constraints

Expected files

swap_str.c

Allowed functions

None. Write every helper yourself.

Allowed headers

<stddef.h>defines NULL

swap_str

Pointers12

Objective

Write a function that exchanges the two char * pointers held at two addresses, without touching a single character of either string.

Steps

a and b are the addresses of two char * variables, so the two strings in play are *a and *b.
Exchange those two pointers: after the call *a holds the pointer that was in *b, and *b holds the pointer that was in *a. One local char * is enough to hold the value being moved.
Copy nothing. The characters of both strings stay exactly where they were, only the two pointers move. No library call is allowed here.
*a or *b may be an empty string or NULL. Move it like any other pointer.
swap_str(&x, &x) is a legal call and must leave x pointing at the string it already pointed at.
When a is NULL or b is NULL, do nothing and return.

examples

$ a = "alpha", b = "beta", swap_str(&a, &b)

a=[beta] b=[alpha]

$ a = "", b = "cargo build --release", swap_str(&a, &b)

a=[cargo build --release] b=[]

$ a points at one[] = "alpha", b points at two[] = "beta", swap_str(&a, &b)

one=[alpha] two=[beta] a=[beta] b=[alpha]

$ a = "git bisect", swap_str(&a, &a)

a=[git bisect]

$ b = "make -j8", swap_str(NULL, &b)

b=[make -j8]

Constraints

Expected files

swap_str.c

Allowed functions

None. Write every helper yourself.

Allowed headers

<stddef.h>defines NULL

Tests

Run the tests to grade your code

Build

01Two ordinary strings

02Lengths far apart

03One character each

04Empty string on the left

05Empty string on the right

06Both strings empty

07Same address on both sides

08Equal contents, the pointers still move

09No character is copied

10A NULL string pointer moves too

11A NULL string pointer moves the other way

12a is NULL, nothing happens

13b is NULL, nothing happens

14Both arguments NULL, no crash