INFO: Common Programming Errors in the C Language

• Microsoft C for MS-DOS, versions 5.1, 6.0, 6.0a, 6.0ax
• Microsoft C/C++ for MS-DOS
• Microsoft Visual C++ for Windows, 16-bit edition, versions 1.0, 1.5
• Microsoft Visual C++, 32-bit Editions, versions 1.0, 2.0, 4.0, 5.0, 6.0

SUMMARY

The text below lists some of the most common errors that occur programming in the C language. Any one of these items can cause unpredictable results, such as invalid data. Some are caught by the compiler and reported as errors or warnings.

• Using an automatic variable that has not been initialized



• Omitting a closing comment delimiter



• Using an array index greater than the length of the array (In C, array indexes run from zero to <length>-1.)



• Omitting a semicolon or a closing brace



• Using an uninitialized pointer



• Using a forward slash when a backslash is required (for example, substituting "/n" for "\n.")



• Using "=" in a comparison where "==" is desired



• Overwriting the null terminator for a string



• Prematurely terminating a function declaration with a semicolon (The compiler often flags the "orphan" block of code as a syntax error.)



• Specifying the values of variables in a scanf() statement instead of their addresses



• Failing to declare the return type for a function



• Assuming an expression evaluation order when using an expression with side effects (For example, a[i] = i++; is ambiguous and dangerous.)



• Failing to account that a static variable in a function is initialized only once



• Omitting a "break" from a case in a switch statement (Execution "falls through" to subsequent cases.)



• Using "break" to exit a block of code associated with an if statement (The break statement exits a block of code associated with a for, switch, or while statement.)



• Comparing a "char" variable against EOF (-1). The following idiom results in an infinite loop when char is unsigned. Note that char is signed by default, so the following will only fail when using the "/J" compiler option:

  
  char c;
  while ((c = getchar()) != EOF)
     {
     } 

Additional query words:

Keywords : kbLangC kbVC100 kbVC150 kbVC200 kbVC400 kbVC500 kbVC600
Version : MS-DOS:; WINDOWS:1.0,1.5; winnt:1.0,2.0,4.0,5.0,6.0
Platform : MS-DOS WINDOWS winnt
Issue type : kbinfo