Methods
fopen
FILE *fopen(const char *filepath, const char *mode)
*filepath should be a relative path or path of target file.
Mode include:
| Mode | Description |
|---|---|
| “r” | Opens a file for reading. The file must exist. |
| “w” | Creates an empty file for writing. If a file with the same name already exists, its content is erased and the file is considered as a new empty file. |
| “a” | Appends to a file. Writing operations, append data at the end of the file. The file is created if it does not exist. |
| “r+” | Opens a file to update both reading and writing. The file must exist. |
| “w+” | Creates an empty file for both reading and writing. |
| “a+” | Opens a file for reading and appending. |
Example:
FILE * fp;
fp = fopen ("file.txt", "r");
fgets
char *fgets(char *str, int n, FILE *stream)
str points to an array where we will store the content we read
n is the maximum length to store the content, n <= length(str)
stream is the object returned from fopen
Notice: it wil stop while meats ‘\n’
Example:
char str[60];
// fp is the content returned from fopen
if( fgets (str, 60, fp)!=NULL ) {
/* writing content to stdout */
puts(str);
}
fscanf
int fscanf(FILE *stream, const char *format, ...)
Similar with fgets but stops if meets any \s
stream is the object returned from fopen
format is the C string that contains one or more of the following items − Whitespace character, Non-whitespace character and Format specifiers. A format specifier will be as [=%[*][width][modifiers]type=], which is explained below
| Sr.No. | Argument | Description |
|---|---|---|
| 1 | * | This is an optional starting asterisk indicates that the data is to be read from the stream but ignored, i.e. it is not stored in the corresponding argument. |
| 2 | width | This specifies the maximum number of characters to be read in the current reading operation. |
| 3 | modifiers | Specifies a size different from int (in the case of d, i and n), unsigned int (in the case of o, u and x) or float (in the case of e, f and g) for the data pointed by the corresponding additional argument: h : short int (for d, i and n), or unsigned short int (for o, u and x) l : long int (for d, i and n), or unsigned long int (for o, u and x), or double (for e, f and g) L : long double (for e, f and g) |
| 4 | type | A character specifying the type of data to be read and how it is expected to be read. See next table. |
type specifiers
type | Qualifying Input | Type of argument
—- | —- | —-
c | Single character: Reads the next character. If a width different from 1 is specified, the function reads width characters and stores them in the successive locations of the array passed as argument. No null character is appended at the end. | char *
d | Decimal integer: Number optionally preceded with a + or - sign | int *
e, E, f, g, G | Floating point: Decimal number containing a decimal point, optionally preceded by a + or - sign and optionally followed by the e or E character and a decimal number. Two examples of valid entries are -732.103 and 7.12e4 | float *
o | Octal Integer |int *
s | String of characters. This will read subsequent characters until a whitespace is found (whitespace characters are considered to be blank, newline and tab). | char *
u | Unsigned decimal integer. | unsigned int *
x, X | Hexadecimal Integer | int *
Additional arguments Depending on the format string, the function may expect a sequence of additional arguments, each containing one value to be inserted instead of each %-tag specified in the format parameter (if any). There should be the same number of these arguments as the number of %-tags that expect a value.
Example:
int main () {
char str1[10], str2[10], str3[10];
int year;
FILE * fp;
fp = fopen ("file.txt", "w+");
fputs("We are in 2012", fp);
rewind(fp);
fscanf(fp, "%s %s %s %d", str1, str2, str3, &year);
printf("Read String1 |%s|\n", str1 );
printf("Read String2 |%s|\n", str2 );
printf("Read String3 |%s|\n", str3 );
printf("Read Integer |%d|\n", year );
fclose(fp);
return(0);
}
Console will show:
Read String1 |We|
Read String2 |are|
Read String3 |in|
Read Integer |2012|
strcmp
int strcmp(const char *str1, const char *str2)
This function return values that are as follows
if Return value < 0 then it indicates str1 is less than str2.
if Return value > 0 then it indicates str2 is less than str1.
if Return value = 0 then it indicates str1 is equal to str2.
So if str1 == str2, it will return 0
