Copying Strings with strcpy()
If you want to copy a string from one array to another, you can copy each item of the first array to the corresponding element in the second array, or you can simply call the C function strcpy() to do the job for you.
The syntax for the strcpy() function is
#include <string.h>
char *strcpy(char *dest, const char *src);
Here the content of the string src is copied to the array referenced by dest. The strcpy() function returns the value of src if it is successful. The header file string.h must be included in your program before the strcpy() function is called.
The program in Listing 13.3 demonstrates how to copy a string from one array to another by either calling the strcpy() function or by doing it yourself.
TYPE
Listing 13.3. Copying strings.
1: /* 13L03.c: Copying strings */
2: #include <stdio.h>
3: #include <string.h>
4:
5: main()
6: {
7: char str1[] = "Copy a string.";
8: char str2[15];
9: char str3[15];
10: int i;
11:
12: /* with strcpy() */
13: strcpy(str2, str1);
14: /* without strcpy() */
15: for (i=0; str1[i]; i++)
16: str3[i] = str1[i];
17: str3[i] = `\0';
18: /* display str2 and str3 */
19: printf("The content of str2: %s\n", str2);
20: printf("The content of str3: %s\n", str3);
21: return 0;
22: }
OUTPUT
After the executable 13L03.exe is created and run, the following output is shown on the screen:
ANALYSIS
C:\app>13L03
The content of str2: Copy a string.
The content of str3: Copy a string.
C:\app>
Three char arrays, str1, str2, and str3, are declared in Listing 13.3. In addition, str1 is initialized with a string constant, "Copy a string.", in line 7.
The statement in line 13 calls the strcpy() function to copy the content of str1 (including the null character appended by the compiler) to the array referenced by str2.
Lines 15_17 demonstrate another way to copy the content of str1 to an array referenced by str3. To do so, the for loop in lines 15 and 16 keeps copying characters of str1 to the corresponding elements in str3 one after another, until the null character (\0) appended by the compiler is encountered. When the null character is encountered, the str1[i] expression used as the condition of the for statement in line 15 returns logical FALSE, which in turn causes the loop to stop.
Because the for loop does not copy the null character from str1 to str3, the statement in line 17 appends a null character to the array referenced by str3. In C, it's very important to make sure that an array that is used to store a string has a null character as its last element.
To prove that the string constant referenced by str1 has been copied to str2 and str3 successfully, the contents held by str2 and str3 are displayed on the screen. Note that the string format specifier %s and the start addresses of str2 and str3 are invoked in the printf() function in lines 19 and 20 to print out all characters, except the null character, stored in str2 or str3. The results displayed on the screen show that str2 and str3 have the exact same content as str1.
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