Functions and Character Double Dimension Array
In this section, you are going to learn
What are the calling conventions of character double dimension array ?
Call by Value
Call by Reference
Revisit Basics : Basics of Character Double Dimension Array
Topics in this section,
char array_name[Row][Column];
Consider a character double dimension array
char a[3][4];
Let us answer few basic questions in this array
If fun(x) is the function call, then fun(typeof(x)) is the prototype / definition
Function Call |
Function Definition |
Observations |
|---|---|---|
fun(a[0][0]) |
void fun(char x) {} |
|
fun(a[1][0]) |
void fun(char x) {} |
|
fun(a[2][0]) |
void fun(char x) {} |
|
fun(&a[0][0]) |
void fun(char *p) { } |
|
fun(&a[1][0]) |
void fun(char *p) { } |
|
fun(&a[2][0]) |
void fun(char *p) { } |
|
fun(**a) |
void fun(char x) {} |
|
fun(*(*(a + 1) + 0)) |
void fun(char x) {} |
|
fun(*(*(a + 2) + 0)) |
void fun(char x) {} |
|
fun(a[0]) |
void fun(char *p) { } |
|
fun(a[1]) |
void fun(char *p) { } |
|
fun(a[2]) |
void fun(char *p) { } |
|
fun(&a[0]) |
void fun(char (*p)[4]) { } |
|
fun(&a[1]) |
void fun(char (*p)[4]) { } |
|
fun(&a[2]) |
void fun(char (*p)[4]) { } |
|
fun(*a) |
void fun(char *p) { } |
|
fun(*(a + 1)) |
void fun(char *p) { } |
|
fun(*(a + 2)) |
void fun(char *p) { } |
|
fun(a) |
void fun(char (*p)[4]) { } |
|
fun(a + 1) |
void fun(char (*p)[4]) { } |
|
fun(a + 2) |
void fun(char (*p)[4]) { } |
|
fun(&a) |
void fun(char (*p)[3][4]) { } |
|
Let us understand the reason behind above prototypes !
If Declaration has two dereference operators, and
Expression has two dereference operators [] [], and
Expression does not have
&then it is call by value
If Declaration has two dereference operators, and
Expression has two dereference operators * *, and
Expression does not have
&then it is call by value
If Declaration has two dereference operators, and
Expression has two dereference operators * [ ], and
Expression does not have
&then it is call by value
Let us look at examples
Step 1 : Consider an array
char a[3][4] = { "lap", "top", "123" };
Condition 1 : Declaration has TWO dereference operators [ ] and [ ]
Step 2 : Consider an expression
a[1][1]
Condition 2 : Expression has TWO dereference operators [ ] and [ ]
Note : [ ] and * are dereference operators
Condition 3 : Expression DOES NOT have & operator
Hence a[1][1] is Call By Value
Step 1 : Consider an array
char a[3][4] = { "lap", "top", "123" };
Condition 1 : Declaration has TWO dereference operators [ ] and [ ]
Step 2 : Consider an expression
**a
Condition 2 : Expression has TWO dereference operators * and *
Note : [ ] and * are dereference operators
Condition 3 : Expression DOES NOT have & operator
Hence **a is Call By Value
If Declaration has two dereference operators, and
Expression has two dereference operators [] [] or * * or [] *, and
Expression has &
then it is call by reference
Example : &a[0][0]
If Declaration has two dereference operators, and
Expression has one dereference operator [ ] or *, and
then it is call by reference
Example : &a[0], a[0], *a
If Declaration has two dereference operators, and
Expression has zero dereference operators, and
then it is call by reference
Example : a, &a, a + 1, a + 2
Step 1 : Consider an array
char a[3][4] = { "lap", "top", "123" };
Condition 1 : Declaration has TWO dereference operators [ ] and [ ]
Step 2 : Consider an expression
&a[1][1]
Condition 2 : Expression has TWO dereference operators * and *
Note : [ ] and * are dereference operators
Condition 3 : Expression has & operator
Hence &a[1][1] is Call By Reference
Step 1 : Consider an array
char a[3][4] = { "lap", "top", "123" };
Condition 1 : Declaration has TWO dereference operators [ ] and [ ]
Step 2 : Consider an expression
a[1]
Condition 2 : Expression has ONE dereference operators
Note : [ ] and * are dereference operators
Condition 3 : Expression DOES NOT have & operator
Hence a[1] is Call By Reference
Let us look at examples of Call by Value
Step 1 : Consider a two dimensional array
char a[3][4] = { "lap", "top", "123" };
Step 2 : Pass a[0][0], a[1][0], a[1][1] to a function
fun
fun(a[0][0]);
fun(a[1][0]);
fun(a[1][1]);
Step 3 : Define function
fun
void fun(char c)
{
printf("char is %c\n", c);
c = 'k';
}
Step 4 : Note that it is call by Value for below reason
Condition 1 : Declaration has TWO dereference operators [ ] and [ ]
Condition 2 : Expression has TWO dereference operators [ ] and [ ]
Condition 3 : Expression DOES NOT have & operator
Means changing value of character inside function DOES NOT affect value of character in Caller !
See full program below
#include <stdio.h>
void fun(char c)
{
printf("char is %c\n", c);
}
int main(void)
{
char a[3][4] = { "lap", "top", "123" };
fun(a[0][0]);
fun(a[1][0]);
fun(a[1][1]);
return 0;
}
Output is as below
char is l
char is t
char is o
Step 1 : Consider a two dimensional array
char a[3][4] = { "lap", "top", "123" };
Step 2 : Pass **a, *(*(a + 1) + 0), *(*(a + 1) + 1) to a function
fun
fun( **a );
fun( *(*(a + 1) + 0) );
fun( *(*(a + 1) + 1) );
Step 3 : Define function
fun
void fun(char c)
{
printf("char is %c\n", c);
c = 'k';
}
Step 4 : Note that it is call by Value for below reason
Condition 1 : Declaration has TWO dereference operators [ ] and [ ]
Condition 2 : Expression has TWO dereference operators * and *
Condition 3 : Expression DOES NOT have & operator
Means changing value of character inside function DOES NOT affect value of character in Caller !
See full program below
#include <stdio.h>
void fun(char c)
{
printf("char is %c\n", c);
}
int main(void)
{
char a[3][4] = { "lap", "top", "123" };
fun( **a );
fun( *(*(a + 1) + 0) );
fun( *(*(a + 1) + 1) );
return 0;
}
Output is as below
char is l
char is t
char is o
Let us look at examples of Call by Reference
Step 1 : Consider a two dimensional array
char a[3][4] = { "lap", "top", "123" };
There are 3 single dimension arrays in char a[3][4]
a[0]
a[1]
a[2]
a[0] is also equal to *a
a[1] is also equal to *(a + 1)
a[2] is also equal to *(a + 2)
a[0] is also equal to &a[0][0]
a[1] is also equal to &a[1][0]
a[2] is also equal to &a[2][0]
Step 2.1 : Method 1 : Pass &a[0][0], &a[1][0], &a[2][0] to a function
fun
fun( &a[0][0] );
fun( &a[1][0] );
fun( &a[2][0] );
Step 2.2 : Method 2 : Pass a[0], a[1], a[2] to a function
fun
fun( a[0] );
fun( a[1] );
fun( a[2] );
Step 2.3 : Method 3 : Pass *a, *(a + 1), *(a + 2) to a function
fun
fun( *a );
fun( *(a + 1) );
fun( *(a + 2) );
Step 3.1 : Define function
fun
void fun(char *ptr)
{
printf("string is %s\n", ptr);
}
Step 4 : Note that it is call by Reference. Means contents of single dimension array can be changed inside function
fun
void fun(char *ptr)
{
strcpy(ptr, "123");
}
See full program below
#include <stdio.h>
void fun(char *ptr)
{
printf("string is %s\n", ptr);
}
int main(void)
{
char a[3][4] = { "lap", "top", "123" };
printf("Method 1 : Access Single dimension arrays\n");
fun( &a[0][0] );
fun( &a[1][0] );
fun( &a[2][0] );
printf("Method 2 : Access Single dimension arrays\n");
fun( a[0] );
fun( a[1] );
fun( a[2] );
printf("Method 3 : Access Single dimension arrays\n");
fun( *a );
fun( *(a + 1) );
fun( *(a + 2) );
return 0;
}
Output is as below
Method 1 : Access Single dimension arrays
string is lap
string is top
string is 123
Method 2 : Access Single dimension arrays
string is lap
string is top
string is 123
Method 3 : Access Single dimension arrays
string is lap
string is top
string is 123
Step 1 : Consider a two dimensional array
char a[3][4] = { "lap", "top", "123" };
There are 3 single dimension arrays in char a[3][4]
a[0]
a[1]
a[2]
Address of single dimension arrays is simply
&a[0]
&a[1]
&a[2]
&a[0] is also equal to a
&a[1] is also equal to a + 1
&a[2] is also equal to a + 2
Step 2.1 : Method 1 : Pass address of single dimension arrays to a function
fun
fun( &a[0] );
fun( &a[1] );
fun( &a[2] );
Step 2.2 : Method 2 : Pass address of single dimension arrays to a function
fun
fun( a );
fun( a + 1 );
fun( a + 2 );
Step 3.1 : Define the function
fun
void fun(char (*ptr)[4] )
{
printf("string is %s\n", *ptr);
}
Step 3.2 : Define the function
funto change the contents of single dimension array
void fun(char (*ptr)[4] )
{
printf("string is %s\n", *ptr);
strcpy((char *)ptr, "Gap");
}
Step 3.3 : Define the function
funto change the contents of single dimension array character by character
void fun(char (*ptr)[4] )
{
printf("string is %s\n", *ptr);
strcpy((char *)ptr, "Gap");
(*ptr)[0] = 'p';
(*ptr)[1] = 'g';
(*ptr)[2] = 'x';
(*ptr)[3] = '\0';
}
See full program below
#include <stdio.h>
void fun(char (*ptr)[4] )
{
printf("string is %s\n", *ptr);
strcpy((char *)ptr, "Gap");
(*ptr)[0] = 'p';
(*ptr)[1] = 'g';
(*ptr)[2] = 'x';
(*ptr)[3] = '\0';
}
int main(void)
{
char a[3][4] = { "lap", "top", "123" };
printf("Method 1 : Access Single dimension arrays\n");
fun( &a[0] );
fun( &a[1] );
fun( &a[2] );
printf("Method 2 : Access Single dimension arrays\n");
fun( a );
fun( a + 1 );
fun( a + 2 );
return 0;
}
Output is as below
Method 1 : Access Single dimension arrays
string is lap
string is top
string is 123
Method 2 : Access Single dimension arrays
string is pgx
string is pgx
string is pgx
Step 1 : Consider a two dimensional array
char a[3][4] = { "lap", "top", "123" };
Step 2 : Pass Address of Double Dimension array to a function
fun(&a);
Step 3.1 : Define function
fun
void fun(char (*ptr)[3][4] )
{
}
Step 3.2 : Access and Print the strings inside function
fun
for (int i = 0 ; i < 3; i++) {
printf("%s\n", (*ptr)[i]);
}
Step 3.3 : Access and Print individual characters inside function
fun
for (int i = 0 ; i < 3; i++) {
for (int j = 0 ; j < 3; j++) {
printf("%c\n", (*ptr)[i][j]);
}
}
Step 3.4 : Access and change strings inside function
fun
for (int i = 0 ; i < 3; i++) {
strcpy( (*ptr)[i], "pgx" );
}
Step 3.5 : Access and change individual characters inside function
fun
for (int i = 0 ; i < 3; i++) {
for (int j = 0 ; j < 3; j++) {
(*ptr)[i][j] = 'c';
}
}
See full program below
#include <stdio.h>
#include <string.h>
void fun(char (*ptr)[3][4] )
{
// Print Individual strings
for (int i = 0 ; i < 3; i++) {
printf("%s\n", (*ptr)[i]);
}
// Print Individual characters
for (int i = 0 ; i < 3; i++) {
for (int j = 0 ; j < 3; j++) {
printf("%c\n", (*ptr)[i][j]);
}
}
// Change Individual strings
for (int i = 0 ; i < 3; i++) {
strcpy( (*ptr)[i], "pgx" );
}
// Change Individual characters
for (int i = 0 ; i < 3; i++) {
for (int j = 0 ; j < 3; j++) {
(*ptr)[i][j] = 'c';
}
}
// Print Individual strings
for (int i = 0 ; i < 3; i++) {
printf("%s\n", (*ptr)[i]);
}
}
int main(void)
{
char a[3][4] = { "lap", "top", "123" };
fun(&a);
return 0;
}
Output is as below
lap
top
123
l
a
p
t
o
p
1
2
3
ccc
ccc
ccc
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