Obtaining Line Numbers in C/C Compilers

When debugging C/C code, it can be useful to determine the line number where an error occurs. A common solution is to manually add line numbers to the code, but a more efficient approach is to use built-in preprocessor macros.

Standard Preprocessor Macros for Line Numbers

The C/C standard defines two preprocessor macros:

• __LINE__: Provides the current line number within the file.
• __FILE__: Gives the current file name.

Example Usage

To print the line number where a logical error occurs, you can use the following code:

if (!Logical) {
  printf("Not logical value at line number %d in file %s\n", __LINE__, __FILE__);
}

Other Preprocessor Variables

In addition to line numbers and file names, other preprocessor variables can be useful for debugging:

• __func__: Returns the name of the current function (supported in C99 but not always in C compilers).
• __DATE__: Provides the current date in the format "Mmm dd yyyy".
• __TIME__: Provides the current time in the format "hh:mm:ss".

Implementation

By incorporating these macros into your code, you can easily obtain line numbers and other debugging information without the need for manual updates. This enhances the accuracy and efficiency of your debugging efforts.