v0.40: Create exercises. Challenge the community.

swap_str

Your mission

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

See it in action

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

Expected result

a=[beta] b=[alpha]

Your checklist

For your own tracking. Tests grade your code.

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.

More examples

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

Expected result

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

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

Expected result

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

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

Expected result

a=[git bisect]

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

Expected result

b=[make -j8]

Constraints

Expected files

swap_str.c

Allowed functions

None. Write every helper yourself.

Allowed headers

<stddef.h>defines NULL

swap_str

Pointers

Your mission

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

See it in action

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

Expected result

a=[beta] b=[alpha]

Your checklist

For your own tracking. Tests grade your code.

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.

More examples

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

Expected result

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

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

Expected result

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

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

Expected result

a=[git bisect]

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

Expected result

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 your code, then check each test here. Open a result to inspect its output.

Build

01Two ordinary stringsWaiting

02Lengths far apartWaiting

03One character eachWaiting

04Empty string on the leftWaiting

05Empty string on the rightWaiting

06Both strings emptyWaiting

07Same address on both sidesWaiting

08Equal contents, the pointers still moveWaiting

09No character is copiedWaiting

10A NULL string pointer moves tooWaiting

11A NULL string pointer moves the other wayWaiting

12a is NULL, nothing happensWaiting

13b is NULL, nothing happensWaiting

14Both arguments NULL, no crashWaiting

swap_str

Your mission

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

See it in action

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

Expected result

a=[beta] b=[alpha]

Your checklist

For your own tracking. Tests grade your code.

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.

More examples

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

Expected result

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

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

Expected result

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

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

Expected result

a=[git bisect]

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

Expected result

b=[make -j8]

Constraints

Expected files

swap_str.c

Allowed functions

None. Write every helper yourself.

Allowed headers

<stddef.h>defines NULL

swap_str

Pointers

Your mission

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

See it in action

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

Expected result

a=[beta] b=[alpha]

Your checklist

For your own tracking. Tests grade your code.

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.

More examples

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

Expected result

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

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

Expected result

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

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

Expected result

a=[git bisect]

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

Expected result

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 your code, then check each test here. Open a result to inspect its output.

Build

01Two ordinary stringsWaiting

02Lengths far apartWaiting

03One character eachWaiting

04Empty string on the leftWaiting

05Empty string on the rightWaiting

06Both strings emptyWaiting

07Same address on both sidesWaiting

08Equal contents, the pointers still moveWaiting

09No character is copiedWaiting

10A NULL string pointer moves tooWaiting

11A NULL string pointer moves the other wayWaiting

12a is NULL, nothing happensWaiting

13b is NULL, nothing happensWaiting

14Both arguments NULL, no crashWaiting

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