【C】 Practical debugging skills

Catalog

debugging

Debug and Release

Shortcut key

View the current information of the program

Debugging cases

How to write good code

Simulate the implementation of library functions ：strcpy

debugging

Novice programmers 80% Time to write code ,20% Time to debug , Old programmer 20% Time to write code ,80% Time to debug .

What is debugging ？

The control code is executed step by step , The process of finding the cause of program errors according to various information is called debugging .

Why debugging is needed ？

When our code goes wrong , Looking only at the surface of the code is often unable to see the problem , We need to see things in the code through debugging .

Debug and Release

The code in our compiler can generate two versions ：Debug and Release.

Before the code is executed , There are only three files in our file

After execution debug edition , More debug file  

Then execute in sequence release edition , More release file

  difference

debug For debug version , It contains debugging information , Without any optimization

release Release version for , Various optimizations have been carried out , Code size and performance are optimal

Shortcut key

F5

Start debugging , Often with F9 Cooperate to jump to the next breakpoint .

F9

Create breakpoints 、 Cancel breakpoint

The breakpoint ： The control program stops , You can also create breakpoints by clicking on the left side of the mouse

Conditional breakpoints ：

Stop when the program meets the set conditions , Often used in cycles .

  example ： Conditional expression , When i ==10 Stop at ,

  When the next breakpoint is this breakpoint , Press down F5, Go straight to i ==10 Stop when .

F10

Deal with one by one , Think of a function as an entire instruction

F11

Inside the function

Ctrl+F5

Directly execute the program without debugging

notes ： If there is Fn Key is required Fn+ The above shortcut keys take effect

Click here for more shortcut keys

View the current information of the program

View temporary variables

  Look at the call stack

Clearly reflect the current function of the function call relationship level

  View assembly information

Check register information  

Debugging cases

What is the output of the following code ？

int main()
{
	int i = 0;
	int arr[10] = { 0 };
	for (i = 0; i <= 12; i++)
	{
		arr[i] = 0;
		printf("Hello");
	}
	return 0;
}

answer ： Dead cycle

Let's explore it through debugging

Through debugging, you can see that in i  be in 0~11 It's all right （ When visiting 0, Set it to 0）, When accessing the twelfth subscript , Come in and find i yes 12, When put arr [12] set 0 When ,i Also became 0, From this we can get the answer ：arr [12] Namely i , When i Is set to 0, Enter the cycle again , This leads to an endless cycle .

  Print out the addresses of the two variables , You can see that their addresses are the same .

Why do you have the same address ？

The way to store data in the stack is to use the high address first and then the low address . And the array grows with the subscript , The address changes from low to high .

  When i and arr When there is a proper distance between , Using the array out of bounds operation, it is possible to cover i . The situation of each compiler is different .

How to write good code

1、 Use assert Avoid null pointers .

2、 Use as much as possible const .

3、 Add necessary comments .

Simulate the implementation of library functions ：strcpy

strcpy Is a function that copies a string into another string variable . Need to include header file <string.h>.

void my_strcpy(char* arr1, char* arr2)
{
	while (*arr2!='\0')
	{
		*arr1 = *arr2;
		arr1++;
		arr2++;
	}
	*arr1 = *arr2;// Will the last '\0' Copy it in, too 
}

First optimization ：

void my_strcpy(char* arr1, char* arr2)
{
	while (*arr2!='\0')
	{
		*arr1++ = *arr2++;// After assignment, directly ++
	}
	*arr1 = *arr2;// Will the last '\0' Copy it in, too 
}

Second optimization ：

void my_strcpy(char* arr1, char* arr2)
{
	while (*arr1++ = *arr2++)//(*arr1++ = *arr2++) Finally, return the assignment character ASCII Code value 
	{                        // Finally, assign values first '\0', Then judge that the cycle condition is false , Exit loop 
		;// Execute an empty statement 
	}
}

Third optimization ：

void my_strcpy(char* arr1, const char* arr2)// Because the assigned string does not need to be changed , therefore const modification 
{
	while (*arr1++ = *arr2++)//(*arr1++ = *arr2++) Finally, return the assignment character ASCII Code value 
	{                        // Finally, assign values first '\0', Then judge that the cycle condition is false , Exit loop 
		;// Execute an empty statement 
	}
}

The fourth optimization ：

void my_strcpy(char* arr1, const char* arr2)// Because the assigned string does not need to be changed , therefore const modification 
{
	assert(arr2 != NULL);// Assertion arr2 Not null pointer , If null pointer , Application error 
	assert(arr1 != NULL);
	while (*arr1++ = *arr2++)//(*arr1++ = *arr2++) Finally, return the assignment character ASCII Code value 
	{                        // Finally, assign values first '\0', Then judge that the cycle condition is false , Exit loop 
		;// Execute an empty statement 
	}
}