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5. Strings as Arrays
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| 5.1 Strings |
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 A string constant, written as "I am a string“ is an array of characters. |
| Strings stored as null-terminated character arrays (last character == ‘\0’) |
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char str[] = “This is a string.”;
char *pc = str;
*(pc+10) = ‘S’;
puts(str); // prints “This is a String.”
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| There is an important difference between the following definitions: |
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char amessage[] = “now is the time”; // an array
char *pmessage = “now is the time”; // a pointer
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| – amessage is an array, just big enough to hold the sequence of characters and '\0' that initializes it. |
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| – pmessage is a pointer, initialized to point to a string constant. |
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| 5.2 String Utility Functions |
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String functions in standard header string.h
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| Type |
Functions |
Meaning |
| Copy |
char *strcpy(strto, strfrom) |
copy strfrom to strto |
| char *strncpy(strto, strfrom, n) |
copy n chars from strfrom to strto |
| Comparison |
int strcmp(str1, str2) |
compare str1, str2; return 0 if equal, positive if str1>str2, negative if str1<str2. |
| int strncmp(str1, str2, n) |
compare first n chars of str1 and str2 |
| Length |
int strlen(str) |
get length of str |
| Concatenation |
char *strcat(strto, strfrom) |
add strfrom to end of strto |
| char *strncat(strto, strfrom, n) |
add n chars form strfrom to endof strto |
| Search |
char *strchr(str, c) |
find char c in str, return pointer to first occurrence, or NULL if no found. |
| char *strrchr(str, c) |
find char c in str, return pointer to last occurrence, or NULL if not found. |
| ... |
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Many other utility functions exist |
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| Example: strcpy() |
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/* strcpy: copy from to to */
* strcpy: array subscript version */
void strcpy(char *to, char *from)
{
int i;
i = 0;
while ((to[i] = from[i]) != ‘\0’)
i++;
}
/* strcpy: pointer version */
void strcpy(char *to, char *from)
{
int i;
i = 0;
while ((*to = *from) != ‘\0’) {
to++;
from++;
}
}
/* strcpy: pointer version 2 */
void strcpy(char *to, char *from)
{
while ((*to++ = *from++) != ‘\0’)
;
}
/* strcpy: pointer version 3 */
void strcpy(char *to, char *from)
{
while (*to++ = *from++)
;
}
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| Example: strcmp() |
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/* strcmp: return <0 if s<t, 0 if s==t, >0 if s>t */
/* strcmp: array version */
int strcmp(char *s, char *t)
{
int i;
for (i=0; s[i]==t[i]; i++)
if (s[i]==‘\0’)
return 0;
return s[i]-t[i];
}
/* strcmp: pointer version */
int strcmp(char *s, char *t)
{
for (; *s==*t; s++, t++)
if (*s==‘\0’)
return 0;
return *s-*t;
}
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