Bifalgorithm post · Computer science one · Character Arrays

How do you dynamically allocate and copy strings in C?

How do you dynamically allocate and copy strings in C? (Computer science one · Character Arrays) — "Just as with int and double types, however, we can dynamica…

Ideas in this flowchart

  • Dynamic allocation of character arrays requires special string-handling rules
  • Character memory can be dynamically allocated with malloc(), just like int and double memory
  • At least one extra character must be allocated for the null-terminating character
  • The example allocates space for 10 characters
  • Because of the terminator, the array can hold only 9 characters of text
  • An entire string cannot be assigned directly to the dynamically allocated array
  • The assignment fullName = "Tom Waits"; is the wrong approach
  • The assignment makes fullName point to the static literal string
  • The original dynamically allocated array is lost, causing a memory leak
  • strcpy() must be used to copy a string into the allocated array
  • The function prototype is char *strcpy(char *dest, const char *src);
  • strcpy() copies the source character sequence into the destination
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How do you dynamically allocate and copy strings in C?

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Computer science one

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"Just as with int and double types, however, we can dynamically allocate memory to hold char types using malloc(). The important difference being that we need to always allocate at least one more character to accommodate the null-terminating character.\n\nchar *fullName = NULL;\n\nfullName = (char *) malloc(sizeof(char) * 10);\n\nThis example creates a dynamically allocated char array that is able to hold 9 characters (since one will be needed for the null-terminating character). However, once we have created the array, we cannot simply assign an entire string to it using the usual assignment operator.\n\n//THIS IS *WRONG*:\n\nfullName = \"Tom Waits\";\n\nThis will compile, but doesn’t give us what we want. Recall that fullName is a character pointer. Using the assignment operator simply makes it point to the static, literal string \"Tom Waits\". In fact, we lose our reference to the dynamically allocated array that was created with malloc(), resulting in a memory leak. Instead, we need to use a function in the standard library to copy a string. The function in the standard library that allows you to copy strings is as follows.\n\nchar *strcpy(char *dest, const char *src);\n\nThe name, strcpy is short for “string copy.” Both arguments are character pointers. In keeping with the use of the assignment operator, the second argument (“source”) is copied into the first, “destination” (just as with an assignment operator, the value)."

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