Difference between Compile Time and Run Time in C

Difference between Compile Time and Run Time in C

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Updated on Mar 16, 2023 17:17 IST

To convert a high-level language program to machine language for execution, a compiler is used, and this process is referred to as compilation. The compiler doesn’t evaluate the program during the translation; it only translates it to machine-level language.

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Errors that occur during program compilation are known as compilation errors, whereas those that happen during program execution are referred to as runtime errors. During runtime, a program is being executed. In this article, we will discuss the difference between compile time and run time in C programming. So, without further ado, let’s get started!

We will be covering the following sections:

Introduction

Computers are only able to understand binary language, which means that if we want to communicate with computers, we have to use binary language. However, writing a program in binary language is not practical, so instead, we write programs in high-level languages. While this is easier for us, computers cannot understand high-level languages. To solve this problem, we use compilers, which translate the high-level code into machine language before execution.

An example of how this works is with robots that are programmed to respond to a specific set of commands. If a command is given that the robot is not programmed to understand, it will not respond correctly. Similarly, computers are only able to understand specific words, and if a command is given that the computer does not know, it will show an error.

Understanding this basic concept will help us to differentiate between compile-time and run-time errors. Compile time refers to the period when the code is being translated by the compiler, while run time refers to the period when the code is being executed.

Difference between Compile Time Errors and Run-Time Errors

Here’s a table summarizing the differences between compile-time errors and runtime errors in C++:

Parameter Compile-time Errors Runtime Errors
Definition Occur during compilation Occur during program execution
Detection Detected by the compiler Detected by the program
Occurrence Occur when syntax or semantic rules are violated Occur when the program encounters unexpected or erroneous conditions during execution
Causes Syntax errors, semantic errors, linker errors Division by zero, null pointer dereference, out-of-bounds array access, memory leaks, and other runtime-specific issues
Debugging Debugging symbols are used to identify and fix errors Debugging tools such as exception handling and tracing are used to identify and fix errors
Impact Prevent the program from running or generating an executable file May cause the program to crash or produce unexpected results during runtime

It is important to note that while compile-time errors are detected and fixed during the development phase, runtime errors can occur even after the program has been released and may require post-release patches or updates to fix.

What is Compile Time?

In C++, compile time refers to the period during which the compiler translates the source code into machine code. During compile time, the compiler checks the syntax of the code and verifies that it is free of errors. If errors are found, the compiler will stop and report them to the programmer.

Compile-time is an important aspect of the software development process, as it ensures that the code is correct and will work as intended when executed. This process also generates an executable file that can be run on a computer.

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Compile Time Errors

Compile-time errors are errors that occur during the compilation process when the source code is being translated by the compiler.

It is important to fix compile-time errors before attempting to execute the program, as these errors will prevent the program from working correctly. Proper code design and careful testing can help to minimize the occurrence of compile-time errors.

There are two main types of compile-time errors:

  • Syntax Errors: These are the most common type of compile-time error, and they occur when the syntax of the code is incorrect. This could be due to spelling mistakes, missing or mismatched brackets, or using incorrect keywords. These errors are usually easy to identify, as the compiler will generate an error message that points to the line in the source code where the error occurred.
  • Semantic Errors: These errors, on the other hand, are less common but more difficult to detect. These errors occur when the code is syntactically correct but does not behave as intended. For example, if a programmer intends to add two numbers but accidentally subtracts them, the code will be syntactically correct but will not behave as intended. These errors can be difficult to detect and often require careful testing and debugging to identify and fix.

Syntax Errors

Let’s look at a few common syntax errors:

  • Missing semicolon

Here’s an example of a missing semicolon error in C++:

 
#include
\n <iostream>\n
\n
int main() {\n
std::cout << "Hello, world!" << std::endl\n
return 0;\n
}\n
\n </iostream>
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In this example, the statement std::endl; is missing a semicolon at the end. When you try to compile this code, you will get an error message similar to the following:

 
main.cpp: In function ‘int main():
main.cpp:5:3: error: expected ‘;’ before ‘return
return 0;
^~~~~~
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The error message indicates that a semicolon is expected before the return statement, but was not found. To fix this error, you just need to add a semicolon at the end of the previous line, like this:

 
#include
\n <iostream>\n
\n
int main() {\n
std::cout << "Hello, world!" << std::endl;\n
return 0;\n
}\n
\n </iostream>
Copy code

Now the code compiles without errors.

  • Missing Parenthesis (})

Here’s an example of a missing parenthesis error in C++:

 
#include
\n <iostream>\n
\n
\n
int main() {\n
int x = 10;\n
int y = 20;\n
int z = x + y;\n
std::cout << "The sum of " << x << " and " << y << " is " << z << std::endl;\n
if (x > y {\n
std::cout << "x is greater than y" << std::endl;\n
}\n
return 0;\n
}\n
\n </iostream>
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In this example, the if statement is missing a closing parenthesis. When you try to compile this code, you will get an error message similar to the following:

 
main.cpp: In function ‘int main():
main.cpp:8:12: error: expected ‘)’ before ‘{’ token
if (x > y {
^
)
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The error message indicates that a closing parenthesis is expected before the opening brace, but was not found. To fix this error, you just need to add a closing parenthesis after y, like this:

 
#include
\n <iostream>\n
\n
\n
int main() {\n
int x = 10;\n
int y = 20;\n
int z = x + y;\n
std::cout << "The sum of " << x << " and " << y << " is " << z << std::endl;\n
if (x > y) {\n
std::cout << "x is greater than y" << std::endl;\n
}\n
return 0;\n
}\n
\n </iostream>
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Now the code compiles without errors.

  • Printing the value of a variable without declaring it

In C++, you cannot print the value of a variable without declaring it. The compiler needs to know the data type of the variable in order to reserve the appropriate amount of memory and perform the necessary operations on it.

If you try to print the value of an undeclared variable, you will get a compile-time error. Here is an example:

 
#include
\n <iostream>\n
\n
\n
int main() {\n
std::cout << x << std::endl;\n
return 0;\n
}\n
\n </iostream>
Copy code

In this example, the variable x is not declared before it is used in the std::cout statement. When you try to compile this code, you will get an error message similar to the following:

 
main.cpp: In function ‘int main():
main.cpp:4:14: error: ‘x’ was not declared in this scope
std::cout << x << std::endl;
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The error message indicates that the variable x was not declared in this scope, meaning it has not been given a data type or reserved memory. To fix this error, you need to declare and initialize the variable before using it, like this:

 
#include
\n <iostream>\n
\n
\n
int main() {\n
int x = 42;\n
std::cout << x << std::endl;\n
return 0;\n
}\n
\n </iostream>
Copy code

Now the code compiles without errors and prints the value of x.

What is Run Time?

In C++, runtime refers to the period during which a compiled program is executed on a computer. Once a program has been compiled, it can be executed or run on a computer. During runtime, the computer loads the program into memory and executes its instructions.

During runtime, the program may encounter errors that are not detected during the compilation process. These errors are known as runtime errors or exceptions and can be caused by a variety of factors, such as incorrect input, memory issues, or hardware problems.

In C++, the runtime environment includes a number of tools and features that can help programmers to detect and diagnose runtime errors. These tools include exception handling, which allows the program to recover from errors and continue executing, and debugging tools that allow programmers to trace the execution of the program and identify potential errors.

Run Time Errors

In C++, runtime errors are errors that occur during the execution of a program, as opposed to compile-time errors which occur during the compilation of the program. These errors are often the result of unexpected or erroneous conditions that arise during the execution of a program.

Runtime errors are generally harder to detect and debug than compile-time errors, as they may not be detected until the program is executed with specific inputs or under specific conditions. Common examples of runtime errors in C++ include:

  • Division by zero: if a program attempts to divide a number by zero, it will result in a runtime error.
  • Out-of-bounds array access: if a program attempts to access an element in an array that is outside the bounds of the array, it will result in a runtime error.
  • Null pointer dereference: if a program attempts to dereference a null pointer, it will result in a runtime error.
  • Memory leaks: if a program allocates memory dynamically and fails to deallocate it properly, it can result in a runtime error.

To handle runtime errors, C++ provides the concept of exception handling. Exception handling allows the program to recover from errors and continue executing, or to terminate gracefully in the event of a catastrophic failure. Exception handling is typically implemented using the try-catch construct, which allows the program to catch and handle specific types of exceptions that may occur during runtime. Additionally, C++ provides various debugging tools that allow programmers to trace the execution of a program and identify potential runtime errors.

Endnotes

In conclusion, in C++ (and most programming languages), errors can be categorized as compile-time errors or run-time errors. Compile-time errors occur during the compilation of the code and are caused by syntax or semantic errors in the code. Run-time errors occur when the program is executing and are caused by issues like division by zero, out of bounds array access, and memory allocation errors.

While compile-time errors can be annoying and time-consuming to fix, they can often be caught and fixed before the program is even run. On the other hand, run-time errors can be more difficult to find and fix, as they often involve complex interactions between different parts of the program.

If you want to learn more about C++ and solidify your basics, you can explore our articles on C++.

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