♦ Finally, the string must have an end.<\/p>\n
The string’s size and its end may seem like the same concepts, but in the C language they’re not. When you assign storage space for a string, you’re allocating a given chunk of memory. The string may or may not occupy that entire space, which is why the string must have a definite stopping point.<\/p>\n
I’ve coded my own string functions in C to handle input or manipulate string constants. The C library function I use most often is strcat()<\/em>, which glues two strings together.<\/p>\n Here’s a chunk of code from a text mode game I wrote. It creates a hidden file in the user’s home directory to store the high scores table:<\/p>\n The first line copies the user’s home directory prefix (obtained from the operating system’s environment table) into a string buffer, The original string buffer, Here’s how the code works with regards to my three rules:<\/p>\n ♦ First, the string needs a location in memory<\/em>.<\/p>\n This job is handled by the ♦ Second, the string has to have a given size. Going along with that is typing the size to store <\/em>char variables.<\/em><\/p>\n This job is handled by the malloc()<\/em> function at Line 9. Storage space for 5 char<\/em> variables is created. That’s four characters for the string plus one for the null character, ♦ Finally, the string must have an end.<\/em><\/p>\n The string is created starting at Line 17. Pointer Finally, at Line 22, the null character is stored at the end of the string. Variable Line 25 displays the result.<\/p>\n I’ve added Figure 1 below to help illustrate how the string is populated. Remember: The key is to cap any string with a null character, Figure 1.<\/strong> How pointer Just as you know to put a period at the end of a sentence for a spoken language, you must remember that a string of text in C ends with a null character. Continue reading strcat(HighScoreFile,homedirprefix);\r\nstrcat(HighScoreFile,\"\/.\");\r\nstrcat(HighScoreFile,HIGH_SCORE_FILENAME);<\/code><\/pre>\nHighScoreFile<\/code>. The second line appends the string constant \/.<\/code> to that buffer. Finally the third line appends the high score filename, referenced by the constant HIGH_SCORE_FILENAME<\/code>, to the buffer. At this point, the string stored in the buffer HighScoreFile<\/code> contains the full pathname to the high score file.<\/p>\nHighScoreFile<\/code>, is a 256-byte chunk of memory designated as a char<\/em> buffer. Such storage is necessary when you build strings from scratch. The following code shows an example, carefully following the three rules mentioned at the start of this Lesson.<\/p>\n\r\n#include <stdio.h>\r\n#include <stdlib.h>\r\n\r\nint main()\r\n{\r\n char *buffer,*b;\r\n\r\n\/* Create a 4-character string buffer *\/\r\n buffer = (char *)malloc(5 * sizeof(char));\r\n if(buffer == NULL)\r\n {\r\n puts(\"Unable to allocate buffer\");\r\n exit(1);\r\n }\r\n\r\n\/* Create the string *\/\r\n b = buffer;\r\n *b++ = 'A';\r\n *b++ = 'B';\r\n *b++ = 'C';\r\n *b++ = 'D';\r\n *b = '\\0';\r\n\r\n\/* Display the string *\/\r\n printf(\"The string \\\"%s\\\" was created\\n\",buffer);\r\n\r\n return(0);\r\n}<\/pre>\nbuffer<\/code> pointer created at Line 6. The pointer is empty, of course, but it’s designed to reference the starting address of an array of char<\/em> variables — a string.<\/p>\n\\0<\/code>. The storage space is typecast to hold char<\/em> variables. That all happens in Line 9.<\/p>\nb<\/code> is initialized to pointer buffer<\/code>‘s address, the start of string storage. Letters A through D are stored in the string; the *b++<\/code> construction stores the character and then increments pointer b<\/code> to reference the next location in the buffer.<\/p>\nb<\/code> doesn’t need to be incremented at that point as it already references the fifth position in the buffer.<\/p>\nThe string \"ABCD\" was created<\/code><\/pre>\n\\0<\/code>. If you use the C library string functions, such as strcat()<\/em>, then the null character is dealt with automatically. Do it yourself, however, and you must remember the \\0<\/code>.<\/p>\n![\"Figure](\"http:\/\/c-for-dummies.com\/blog\/wp-content\/uploads\/2013\/12\/1228-figure1.png\")
b<\/code> creates the string in memory.<\/p><\/div>\n","protected":false},"excerpt":{"rendered":"