Use conditional breakpoints in vscode (based on GDB)

This article tells VSCode How to use conditional breakpoints in , Generally, the breakpoints we use are regular breakpoints , The program stops when it runs , But sometimes you want to trigger a breakpoint only under certain conditions , This requires setting the normal breakpoint to a conditional breakpoint .

Use it directly gdb The instructions of can be found in debug console Set in the , about VSCode, It will be easier to set up .

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One Example program

First, prepare an example program , as follows ,

#include <iostream>
#include <cstdint>

int main(int, char**) {
    
    std::cout << "Hello, world!\n";

    uint32_t index = 0;
    for (; index < 100; ++index)
    {
    
        std::cout << "aaa\n";
    }

    return 0;
}

Then printing “aaa” Add a regular breakpoint where , See the red dot in the figure below ,

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Two Conditional breakpoints

Conditional breakpoints are divided into expressions and Hit Count Two kinds of , Here are the introduction ,

1. Expression breakpoint

Suppose we want the variable index The value is greater than 20 Trigger breakpoints when , Right click the red breakpoint , choice Edit Breakpoint,

The following interface appears ,

Then enter... On the right “index > 20”, This is the expression ,

Then return , Press enter to save the settings , Otherwise, conditional breakpoints will not work , Finally, as follows ,

Then start debugging , Finally, run the program until the breakpoint is triggered , You can see in the local variables window on the left index The value of is 21,

Description of successful operation .

Expressions can be various , As long as the result of the expression is True, Then the breakpoint will be triggered , If there are multiple conditions , Then you can use it && and || Symbol to connect , as follows ,

hope index The value of the 20 and 25 Between , Remember to press enter to save after modification .

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2. Hit Count The breakpoint

Hit Count The number of times the program reaches the line where the breakpoint is located , So this breakpoint means how many times it is triggered when the line is run .

Also right-click the breakpoint , And then choose Edit Breakpoint, At this point, you need to clear out the contents of the expression breakpoint , Then press enter to save it .

Because of this 2 If all configurations are set , Then it won't work , So first clear the contents of the expression breakpoint . as follows , Remember to press enter to save ,

Then right-click the breakpoint again , choice Edit Breakpoint, Then click on “Expression” The arrow on the right expands , as follows ,

choice Hit Count, Then enter a number on the right , Input here 10, as follows ,

Indicates that you want to run the line 10 Trigger after times , Then press enter to save .

Finally, start debugging , And let the program run until the breakpoint is triggered ,

Variable available index The value of proves indirectly whether it has been run so many times , The local variables window on the left is shown below ,

There may be a little doubt here ： perform 10 Time ,index The value of should not be 9 Do you , Why 10？ Because it is to execute 10 Time , That's what we need 10 The breakpoint is triggered only after the execution is completed , So when the break point is triggered , Is ready to execute the 11 Time , That's why index The value of is 10, instead of 9

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3、 ... and summary

This article tells you how to VSCode Use conditional breakpoint debugging in C/C++ Program , It is very convenient and easy to use . For other languages , It's the same thing .