Code written by beginners to C, or found on C programming forums, frequently contains a few specific string handling bugs. Even experienced programmers coming from a higher level language and picking up C may make these mistakes.

These bugs seem to result from expecting C to have a built-in string class (like most languages do) which would handle all string operations and memory allocation for them.

Here are some frequently occurring bugs with corresponding questions:

1. char str = "hello";.

   This will luckily not even compile if the compiler is configured correctly, see What compiler options are recommended for beginners learning C?

   Question: Why doesn't this work? Does C have a string class?

2. char str[5] = "hello";.

   Compiles just fine, yet when printing this there will be garbage printed or other strange behavior. This bug is related to character arrays and missing null termination.

   Question: What exactly does a string consist of in C?

3. char* str; scanf("%s", str);

   Compiles just fine, though if lucky there can be warnings. This bug is related to memory allocation.

   Question: Who is responsible for allocating memory for the string?

4. char* str = malloc(5+1); str = "hello";

   Compiles just fine, though there are memory leaks.

   Question: How can a string get assigned a new value?

5. char str[5+1] = "hello"; ... if(str == "hello").

   Compiles just fine but gives the wrong results.

   Question: How do you properly compare strings?

posted about 3 years ago

CC BY-SA 4.0

8d ago by Karl Knechtel‭

Lundin‭

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