HP C/iX Library Reference Manual (30026-90004)

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336 Chapter5

HP C/iX Library Function Descriptions

strcpy

character early in the program. The ﬁrst chr element is then successively set to the next

lowercase character in the for loop, and the resulting two-character string is concatenated

onto the end of the alphabet assembled so far in alpha. Note the use of strcpy() to

initialize alpha. Remember that C transforms one or more characters enclosed in double

quotation marks into a character pointer to those characters followed by a null character.

Thus, the strcpy() statement above copies the character 'a' followed by a null character

into alpha.

There are some things to be aware of when using strcpy(), strncpy(), strcat(), and

strncat(). These functions all modify string

in some way, but none of them check for

overﬂow in that string. Therefore, be sure there is enough room in

to hold the added or

copied characters plus a terminating null character. Also, be sure you use a character

array

for

(not just a character pointer), especially when using strcat or strncat. This

is because an explicitly declared array can have sufﬁcient memory allocated to it to contain

all of its elements, but a character pointer simply points to a single location in memory.

Concatenating a string to the end of a string contained in an array is guaranteed to work if

the array is large enough. However, concatenating a string to a string of characters

referenced by a simple character pointer is dangerous, because the concatenated

characters could overwrite data in memory. For example,

char array[100], *ptr = "abcdef";

…

strcat(array, ptr);

works ﬁne, because you are guaranteed that 100 storage elements have been set aside for

the array. However,

char *ptr1 = "abcdef", *ptr2 = "ghijkl";

…

strcat(ptr1, ptr2);

will not work. Although C makes sure there is enough room for the initializing strings

("abcdef" and "ghijkl" in this example), there are no guarantees that there is enough room

to add characters to the end of one of these strings. Therefore, the last fragment could

easily overwrite valid data occurring after the string pointed to by ptr1.

Because string

is not modiﬁed, you can use arrays or character pointers for this item

with no ill effects.