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This section gives some program examples that show how the I/O functions can be used in applications.
Example 2-1 shows the printf function.
| Example 2-1 Output of the Conversion Specifications | |||
|---|---|---|---|
/* CHAP_2_OUT_CONV.C */
/* This program uses the printf function to print the */
/* various conversion specifications and their effect */
/* on the output. */
/* Include the proper header files in case printf has */
/* to return EOF. */
#include <stdlib.h>
#include <stdio.h>
#include <wchar.h>
#define WIDE_STR_SIZE 20
main()
{
double val = 123345.5;
char c = 'C';
int i = -1500000000;
char *s = "thomasina";
wchar_t wc;
wchar_t ws[WIDE_STR_SIZE];
/* Produce a wide character and a wide character string */
if (mbtowc(&wc, "W", 1) == -1) {
perror("mbtowc");
exit(EXIT_FAILURE);
}
if (mbstowcs(ws, "THOMASINA", WIDE_STR_SIZE) == -1) {
perror("mbstowcs");
exit(EXIT_FAILURE);
}
/* Print the specification code, a colon, two tabs, and the */
/* formatted output value delimited by the angle bracket */
/* characters (<>). */
printf("%%9.4f:\t\t<%9.4f>\n", val);
printf("%%9f:\t\t<%9f>\n", val);
printf("%%9.0f:\t\t<%9.0f>\n", val);
printf("%%-9.0f:\t\t<%-9.0f>\n\n", val);
printf("%%11.6e:\t\t<%11.6e>\n", val);
printf("%%11e:\t\t<%11e>\n", val);
printf("%%11.0e:\t\t<%11.0e>\n", val);
printf("%%-11.0e:\t\t<%-11.0e>\n\n", val);
printf("%%11g:\t\t<%11g>\n", val);
printf("%%9g:\t\t<%9g>\n\n", val);
printf("%%d:\t\t<%d>\n", c);
printf("%%c:\t\t<%c>\n", c);
printf("%%o:\t\t<%o>\n", c);
printf("%%x:\t\t<%x>\n\n", c);
printf("%%d:\t\t<%d>\n", i);
printf("%%u:\t\t<%u>\n", i);
printf("%%x:\t\t<%x>\n\n", i);
printf("%%s:\t\t<%s>\n", s);
printf("%%-9.6s:\t\t<%-9.6s>\n", s);
printf("%%-*.*s:\t\t<%-*.*s>\n", 9, 5, s);
printf("%%6.0s:\t\t<%6.0s>\n\n", s);
printf("%%C:\t\t<%C>\n", wc);
printf("%%S:\t\t<%S>\n", ws);
printf("%%-9.6S:\t\t<%-9.6S>\n", ws);
printf("%%-*.*S:\t\t<%-*.*S>\n", 9, 5, ws);
printf("%%6.0S:\t\t<%6.0S>\n\n", ws);
}
|
Running Example 2-1 produces the following output:
$ RUN EXAMPLE %9.4f: <123345.5000> %9f: <123345.500000> %9.0f: < 123346> %-9.0f: <123346 > %11.6e: <1.233455e+05> %11e: <1.233455e+05> %11.0e: < 1e+05> %-11.0e: <1e+05 > %11g: < 123346> %9g: < 123346> %d: <67> %c: <C> %o: <103> %x: <43> %d: <-1500000000> %u: <2794967296> %x: <a697d100> %s: <thomasina> %-9.6s: <thomas > %-*.*s: <thoma > %6.0s: < > %C: <W> %S: <THOMASINA> %-9.6S: <THOMAS > %-*.*S: <THOMA > %6.0S: < > $ |
Example 2-2 shows the use of the fopen , ftell , sprintf , fputs , fseek , fgets , and fclose functions.
| Example 2-2 Using the Standard I/O Functions | |||
|---|---|---|---|
/* CHAP_2_STDIO.C */
/* This program establishes a file pointer, writes lines from */
/* a buffer to the file, moves the file pointer to the second */
/* record, copies the record to the buffer, and then prints */
/* the buffer to the screen. */
#include <stdio.h>
#include <stdlib.h>
main()
{
char buffer[32];
int i,
pos;
FILE *fptr;
/* Set file pointer. */
fptr = fopen("data.dat", "w+");
if (fptr == NULL) {
perror("fopen");
exit(EXIT_FAILURE);
}
for (i = 1; i < 5; i++) {
if (i == 2) /* Get position of record 2. */
pos = ftell(fptr);
/* Print a line to the buffer. */
sprintf(buffer, "test data line %d\n", i);
/* Print buffer to the record. */
fputs(buffer, fptr);
}
/* Go to record number 2. */
if (fseek(fptr, pos, 0) < 0) {
perror("fseek"); /* Exit on fseek error. */
exit(EXIT_FAILURE);
}
/* Read record 2 in the buffer. */
if (fgets(buffer, 32, fptr) == NULL) {
perror("fgets"); /* Exit on fgets error. */
exit(EXIT_FAILURE);
}
/* Print the buffer. */
printf("Data in record 2 is: %s", buffer);
fclose(fptr); /* Close the file. */
}
|
Running Example 2-2 produces the following result:
$ RUN EXAMPLE Data in record 2 is: test data line 2 |
The output to DATA.DAT from Example 2-2 is:
test data line 1 test data line 2 test data line 3 test data line 4 |
| Example 2-3 Using Wide Character I/O Functions | |||
|---|---|---|---|
/* CHAP_2_WC_IO.C */
/* This program establishes a file pointer, writes lines from */
/* a buffer to the file using wide-character codes, moves the */
/* file pointer to the second record, copies the record to the */
/* wide-character buffer, and then prints the buffer to the */
/* screen. */
#include <stdio.h>
#include <stdlib.h>
#include <wchar.h>
main()
{
char flat_buffer[32];
wchar_t wide_buffer[32];
wchar_t format[32];
int i,
pos;
FILE *fptr;
/* Set file pointer. */
fptr = fopen("data.dat", "w+");
if (fptr == NULL) {
perror("fopen");
exit(EXIT_FAILURE);
}
for (i = 1; i < 5; i++) {
if (i == 2) /* Get position of record 2. */
pos = ftell(fptr);
/* Print a line to the buffer. */
sprintf(flat_buffer, "test data line %d\n", i);
if (mbstowcs(wide_buffer, flat_buffer, 32) == -1) {
perror("mbstowcs");
exit(EXIT_FAILURE);
}
/* Print buffer to the record. */
fputws(wide_buffer, fptr);
}
/* Go to record number 2. */
if (fseek(fptr, pos, 0) < 0) {
perror("fseek"); /* Exit on fseek error. */
exit(EXIT_FAILURE);
}
/* Put record 2 in the buffer. */
if (fgetws(wide_buffer, 32, fptr) == NULL) {
perror("fgetws"); /* Exit on fgets error. */
exit(EXIT_FAILURE);
}
/* Print the buffer. */
printf("Data in record 2 is: %S", wide_buffer);
fclose(fptr); /* Close the file. */
}
|
Running Example 2-3 produces the following result:
$ RUN EXAMPLE Data in record 2 is: test data line 2 |
The output to DATA.DAT from Example 2-3 is:
test data line 1 test data line 2 test data line 3 test data line 4 |
Example 2-4 shows the use of both a file pointer and a file descriptor to access a single file.
| Example 2-4 I/O Using File Descriptors and Pointers | |||
|---|---|---|---|
/* CHAP_2_FILE_DIS_AND_POINTER.C */
/* The following example creates a file with variable-length */
/* records (rfm=var) and the carriage-return attribute (rat=cr).*/
/* */
/* The program uses creat to create and open the file, and */
/* fdopen to associate the file descriptor with a file pointer. */
/* After using the fdopen function, the file must be referenced */
/* using the Standard I/O functions. */
#include <unixio.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define ERROR 0
#define ERROR1 -1
#define BUFFSIZE 132
main()
{
char buffer[BUFFSIZE];
int fildes;
FILE *fp;
if ((fildes = creat("data.dat", 0, "rat=cr",
"rfm=var")) == ERROR1) {
perror("DATA.DAT: creat() failed\n");
exit(EXIT_FAILURE);
}
if ((fp = fdopen(fildes, "w")) == NULL) {
perror("DATA.DAT: fdopen() failed\n");
exit(EXIT_FAILURE);
}
while (fgets(buffer, BUFFSIZE, stdin) != NULL)
if (fwrite(buffer, strlen(buffer), 1, fp) == ERROR) {
perror("DATA.DAT: fwrite() failed\n");
exit(EXIT_FAILURE);
}
if (fclose(fp) == EOF) {
perror("DATA.DAT: fclose() failed\n");
exit(EXIT_FAILURE);
}
}
|
Table 3-1 describes the character, string, and argument-list functions in the HP C Run-Time Library (RTL). Although further discussion follows in this chapter, see the Reference Section for more detailed information on each function.
| Function | Description |
|---|---|
| Character Classification | |
| isalnum , iswalnum | Returns a nonzero integer if its argument is one of the alphanumeric characters in the current locale. |
| isalpha , iswalpha | Returns a nonzero integer if its argument is one of the alphabetic characters in the current locale. |
| isascii | Returns a nonzero integer if its argument is any ASCII character. |
| iscntrl , iswcntrl | Returns a nonzero integer if its argument is a control character in the current locale. |
| isdigit , iswdigit | Returns a nonzero integer if its argument is a digit character in the current locale. |
| isgraph , iswgraph | Returns a nonzero integer if its argument is a graphic character in the current locale. |
| islower , iswlower | Returns a nonzero integer if its argument is a lowercase character in the current locale. |
| isprint , iswprint | Returns a nonzero integer if its argument is a printing character in the current locale. |
| ispunct , iswpunct | Returns a nonzero integer if its argument is a punctuation character in the current locale. |
| isspace , iswspace | Returns a nonzero integer if its argument is a white-space character in the current locale. |
| isupper , iswupper | Returns a nonzero integer if its argument is an uppercase character in the current locale. |
| iswctype | Returns a nonzero integer if its argument has the specified property. |
| isxdigit , iswxdigit | Returns a nonzero integer if its argument is a hexadecimal digit (0 to 9, A to F, or a to f). |
| Character Conversion | |
| btowc | Converts a one-byte multibyte character to a wide character in the initial shift state. |
| ecvt, fcvt, gcvt | Converts an argument to a null-terminated string of ASCII digits and return the address of the string. |
| index, rindex | Searches for a character in a string. |
| mblen , mbrlen | Determines the number of bytes in a multibyte character. |
| mbsinit | Determines whether an mbstate_t object decribes an initial conversion state. |
| mbstowcs | Converts a sequence of multibyte characters into a sequence of corresponding codes. |
| toascii | Converts its argument, an 8-bit ASCII character, to a 7-bit ASCII character. |
| tolower, _tolower, towlower | Converts its argument, an uppercase character, to lowercase. |
| toupper, _toupper, towupper | Converts its argument, a lowercase character, to uppercase. |
| towctrans | Maps one wide character to another according to a specified mapping descriptor. |
| wcstombs | Converts a sequence of wide-character codes corresponding to multibyte characters to a sequence of multibyte characters. |
| wctob | Determines if a wide character corresponds to a single-byte multibyte character and returns its multibyte character representation. |
| wctomb | Converts a wide character to its multibyte character representation. |
| wctrans | Returns the description of a mapping, corresponding to specified property, that can be later used in a call to towctrans . |
| wctype | Converts a valid character class defined for the current locale to an object of type wctype_t . |
| String Manipulation | |
| atof | Converts a given string to a double-precision number. |
| atoi, atol | Converts a given string of ASCII characters to the appropriate numeric values. |
| atoll, atoq (ALPHA, I64) | Converts a given string of ASCII characters to an __int64 . |
| basename | Returns the last component of a path name. |
| dirname | Reports the parent directory name of a file path name. |
| strcat, strncat, wcscat, wcsncat | Appends one string to the end of another string. |
| strchr, strrchr, wcschr, wcsrchr | Returns the address of the first or last occurrence of a given character in a null-terminated string. |
| strcmp, strncmp, strcoll, wcscmp, wcsncmp, wcscoll | Compares two character strings and returns a negative, zero, or positive integer indicating that the values of the individual characters in the first string are less than, equal to, or greater than the values in the second string. |
| strcpy, strncpy, wcscpy, wcsncpy | Copies all or part of one string into another. |
| strxfrm, wcsxfrm | Transforms a multibyte string to another string ready for comparisons using the strcmp or wcscmp function. |
| strcspn, wcscspn | Searches a string for a character that is in a specified set of characters. |
| strlen, wcslen | Returns the length of a string of characters. The returned length does not include the terminating null character (\0). |
| strpbrk, wcspbrk | Searches a string for the occurrence of one of a specified set of characters. |
| strspn, wcsspn | Searches a string for the occurrence of a character that is not in a specified set of characters. |
| strstr, wcswcs | Searches a string for the first occurrence of a specified set of characters. |
| strtod, wcstod | Converts a given string to a double-precision number. |
| strtok, wcstok | Locates text tokens in a given string. |
| strtol, wcstol | Converts the initial portion of a string to a signed long integer. |
| strtoll, strtoq (ALPHA, I64) | Converts the initial portion of a string to signed __int64 . |
| strtoul, wcstoul | Converts the initial portion of a string to an unsigned long integer. |
| strtoull, strtouq (ALPHA, I64) | Converts the initial portion of the string pointed to by the pointer to the character string to an unsigned __int64 . |
| String Handling---Accessing Binary Data | |
| bcmp | Compares byte strings. |
| bcopy | Copies byte strings. |
| bzero | Copies nulls into byte strings. |
| memchr, wmemchr | Locates the first occurrence of the specified byte within the initial length of the object to be searched. |
| memcmp, wmemcmp | Compares two objects byte by byte. |
| memcpy, memmove, wmemcpy, wmemmove | Copies a specified number of bytes from one object to another. |
| memset, wmemset | Sets a specified number of bytes in a given object to a given value. |
| Argument-List Handling---Accessing a Variable-Length Argument List | |
| va_arg | Returns the next item in the argument list. |
| va_count | Returns the number of longwords (VAX ONLY) or quadwords (ALPHA ONLY) in the argument list. |
| va_end | Finishes the va_start session. |
| va_start, va_start_1 | Initializes a variable to the beginning of the argument list. |
| vfprintf, vprintf, vsprintf | Prints formatted output based on an argument list. |
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