C ++ Lesson 7 - Extended function parameters

This article learn from Ditai Software College Tangzuo Lin teacher of C ++ courses

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Introduction: C ++ to C function arguments in the upgrade and expansion done, provides default parameters and parameter placeholders. Positional parameters for non-standard compatibility written in C

Experiment 1: The default parameter values
Experiment 2: usage rule arguments
Experiment 3: Error Model function parameters
Experiment 4: in C and C ++ Comparative FUNC () and func (void) are equivalent
Experiment 5: parameter placeholder non-standard compatible written in C
experiment 6: positional parameters with default parameter values and not written specification compatible for use in C

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Answer: The default parameter values ​​can only be specified in the statement, without giving a longer definition.

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Experiment 1: Use the default parameter values

#include <stdio.h>

int mul(int x = 0);//函数参数的默认值

int main(int argc, char *argv[])
{
    printf("%d\n", mul());
    printf("%d\n", mul(-1));
    printf("%d\n", mul(2));
    
    return 0;
}

int mul(int x)
{
    return x * x;
}


mhr@ubuntu:~/work/c++$ g++ 7-1.cpp
mhr@ubuntu:~/work/c++$ ./a.out 
0
1
4
mhr@ubuntu:~/work/c++$ 

Experiment 2: function parameters using rules

#include <stdio.h>

int add(int x, int y = 0, int z = 0);

int main(int argc, char *argv[])
{
    printf("%d\n", add(1));
    printf("%d\n", add(1, 2));
    printf("%d\n", add(1, 2, 3));
    
    return 0;
}

int add(int x, int y, int z)
{
    return x + y + z;
}

mhr@ubuntu:~/work/c++$ 
mhr@ubuntu:~/work/c++$ g++ 7-2.cpp
mhr@ubuntu:~/work/c++$ ./a.out 
1
3
6
mhr@ubuntu:~/work/c++$ 

Experiment 3: Demonstration error function argument

#include <stdio.h>

int add(int x, int y = 0, int z);

int main(int argc, char *argv[])
{
    printf("%d\n", add(1));
    printf("%d\n", add(1, 2));
    printf("%d\n", add(1, 2, 3));
    
    return 0;
}

int add(int x, int y, int z)
{
    return x + y + z;
}


mhr@ubuntu:~/work/c++$ g++ 7-2.cpp
7-2.cpp:3:5: error: default argument missing for parameter 3 of ‘int add(int, int, int)’
 int add(int x, int y = 0, int z);
     ^
mhr@ubuntu:~/work/c++$ 

In the design function default parameters, it can only be considered from right to left to provide default values ​​provided here is from the middle of error.

change

In embodiment C, two types are not equivalent, the former could accept any parameter, which represents takes no parameters.

Experiment 4: in C and C ++ Comparative FUNC () and func (void) are equivalent

In C

Question: Why is this so?
Answer: because there are many non-standard written in C language, as described above experiment, the parameter C language function FUNC () represents, any acceptable parameters, while func (void) represents only takes no arguments! !

In C ++

Therefore, in C ++ FUNC () and func (void) is equivalent to, any parameters are not accepted.

Conclusion:
1. C language compiler parameter function FUNC () represents, any acceptable parameters, while func (void) represents only takes no arguments! ! The two are not equivalent.

2. In the C ++ compiler FUNC () and func (void) is equivalent to, any parameters are not accepted.

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Experiment 5: C irregularities written place holders for parameters compatible

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Experiment 6: positional parameters with default parameter values ​​and non-standard C-compatible for use in the wording

#include <stdio.h>

int func(int x, int = 0);

int main(int argc, char *argv[])
{
    printf("%d\n", func(1));
    printf("%d\n", func(2, 3));
    
    return 0;
}

int func(int x, int)
{
    return x;
}

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