Preface: This is a self-answered Q&A meant as a C string handling FAQ. It will ask several question at once which isn't ideal, but they are all closely related and I'd rather not fragment the post into several.

When reading C programming forums or code written by beginners, there is a number of frequently recurring bugs related to string handling. These are not only written by complete beginners, but as often by experienced programmers coming from a higher level language and picking up C.

The common bugs originates from them assuming that C like most languages has a built-in string class which will handle all string handling and memory allocation for them. Here follows some frequently occurring bugs and their related questions:

• Bug 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?

• Bug 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?

• Bug 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?

• Bug 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?

• Bug 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 over 2 years ago

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Lundin‭

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