c string copy

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c string copy

strdup

  • #include <string.h>
  • char *strdup(const char *s1);

intro

  • return a pointer to a new string, which is a duplicate of the string pointed to by s1. The returned pointer can be passed to free().
  • A null pointer is returned if the new string cannot be created.

    return

  • return a pointer to a new string on success
  • a null pointer and set errno to indicate the error.

e.g.

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#include <string.h>

const char *stringA = "foo";
char *stringB = NULL;

stringB = strdup(stringA);
/* ... */
free(stringB);

reference

strcpy

  • #include <string.h>
  • char *strcpy(char *restrict s1, const char *restrict s2);

intro

  • you need to allocate space first, which isn’t hard to do but can lead to an overflow error, if not done correctly:

    return

  • return s1
  • no return value is reserved to indicate an error.

    e.g.

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    #include <string.h>

    const char *stringA = "foo";
    char *stringB = NULL;

    /* you must add one to cover the byte needed for the terminating null character */
    stringB = (char *) malloc( strlen(stringA) + 1 ); 
    strcpy( stringB, stringA );
    /* ... */
    free(stringB);

    strncpy

    • #include <string.h>
    • char *strncpy(char *s1, const char *s2, size_t n);

    intro

  • copies not more than n bytes (bytes that follow a null byte are not copied) from the array pointed to by s2 to the array pointed to by s1.
  • If copying takes place between objects that overlap, the behaviour is undefined.

    return

  • returns s1
  • no return value is reserved to indicate an error.

    e.g.

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    #include <string.h>

    const char *stringA = "foo";
    char *stringB = NULL;

    /* you must add one to cover the byte needed for the terminating null character */
    stringB = (char *) malloc( strlen(stringA) + 1 ); 
    strcpy( stringB, stringA );
    /* ... */
    free(stringB);

    reference

  • c++ - Proper way to copy C strings - Stack Overflow