C Standard Library -<string.h>
Introduction
string .hThe header file defines a variable type, a macro, and various functions for operating on character arrays.
<string.h>Is a header file in the C standard library, providing a set of functions for handling strings and memory blocks. These functions cover string copying, concatenation, comparison, searching, and memory operations, etc.
Library variables
Below is the variable type defined in the header file string.h:
| Serial Number | Variables & Description |
|---|---|
| 1 | size_t This is an unsigned integer type, which issizeofResult of the keyword. |
Library macros
Below are the macros defined in the header file string.h:
| Serial Number | Macros & Description |
|---|---|
| 1 | NULL This macro is the value of a null pointer constant. |
Library functions
Below are the functions defined in the header file string.h:
| Serial Number | Functions & Description |
|---|---|
| 1 | void *memchr(const void *str, int c, size_t n) In the parameterstrSearches for the first occurrence of character c (an unsigned character) in the first n bytes of the string pointed to. |
| 2 | int memcmp(const void *str1, const void *str2, size_t n) holdstr1andstr2Compares the first n bytes. |
| 3 | void *memcpy(void *dest, const void *src, size_t n) Copies n characters from src todest。 |
| 4 | void *memmove(void *dest, const void *src, size_t n) another used to copy fromsrccopy n characters todestof the function. |
| 5 | void *memset(void *str, int c, size_t n) Copies the specified value c to the first n bytes of the memory area pointed to by str. |
| 6 | char *strcat(char *dest, const char *src) holdsrcAppends the string pointed to bydestTo the end of the string pointed to by |
| 7 | char *strncat(char *dest, const char *src, size_t n) holdsrcAppends the string pointed to bydestthe end of the string it points to, up to a length of n characters. |
| 8 | char *strchr(const char *str, int c) In the parameterstrSearches for the first occurrence of character c (an unsigned character) in the string pointed to. |
| 9 | int strcmp(const char *str1, const char *str2) holdstr1The string pointed to bystr2Compares with the string pointed to by |
| 10 | int strncmp(const char *str1, const char *str2, size_t n) holdstr1andstr2for comparison, comparing at most the first n bytes. |
| 11 | int strcoll(const char *str1, const char *str2) holdstr1andstr2Compares, and the result depends on the LC_COLLATE locale setting. |
| 12 | char *strcpy(char *dest, const char *src) holdsrcthe string pointed to by is copied todest。 |
| 13 | char *strncpy(char *dest, const char *src, size_t n) holdsrcthe string pointed to by is copied todest, copying at most n characters. |
| 14 | size_t strcspn(const char *str1, const char *str2) Counts how many consecutive characters at the beginning of string str1 contain none of the characters in string str2. |
| 15 | char *strerror(int errnum) Searches the internal array for the error number errnum and returns a pointer to the error message string. |
| 16 | size_t strlen(const char *str) Calculates the length of string str, up to but not including the null terminating character. |
| 17 | char *strpbrk(const char *str1, const char *str2) Search stringstr1The first matching string instr2a character from the characters, not including the null terminating character. That is, it examines the characters in string str1 one by one; when a tested character is also found in string str2, it stops and returns the position of that character. |
| 18 | char *strrchr(const char *str, int c) In the parameterstrSearches for the last occurrence of character c (an unsigned character) in the string pointed to. |
| 19 | size_t strspn(const char *str1, const char *str2) Search stringstr1The first character in ... that is not in the stringstr2The index of the character appearing in |
| 20 | char *strstr(const char *haystack, const char *needle) In the stringhaystackFinds the first occurrence of the stringneedle(not including the null terminating character). |
| 21 | char *strtok(char *str, const char *delim) Split stringstras a set of strings,delimas the delimiter. |
| 22 | size_t strxfrm(char *dest, const char *src, size_t n) Converts the string according to the LC_COLLATE category of the program's current locale.srcthe frontnCharacters, and places them in the stringdestIn. |
Example
The following is using<string.h>Examples of some functions in
Copying strings:
Example
#include <stdio.h>
#include <string.h>
int main() {
char src[] = "Hello, World!";
char dest[50];
strcpy(dest, src);
printf("Copied string: %s\n", dest);
return 0;
}
#include <string.h>
int main() {
char src[] = "Hello, World!";
char dest[50];
strcpy(dest, src);
printf("Copied string: %s\n", dest);
return 0;
}
Concatenating strings:
Example
#include <stdio.h>
#include <string.h>
int main() {
char str1[50] = "Hello";
char str2[] = ", World!";
strcat(str1, str2);
printf("Concatenated string: %s\n", str1);
return 0;
}
#include <string.h>
int main() {
char str1[50] = "Hello";
char str2[] = ", World!";
strcat(str1, str2);
printf("Concatenated string: %s\n", str1);
return 0;
}
Comparing strings:
Example
#include <stdio.h>
#include <string.h>
int main() {
char str1[] = "Hello";
char str2[] = "World";
int result = strcmp(str1, str2);
if (result == 0) {
printf("Strings are equal\n");
} else {
printf("Strings are not equal\n");
}
return 0;
}
#include <string.h>
int main() {
char str1[] = "Hello";
char str2[] = "World";
int result = strcmp(str1, str2);
if (result == 0) {
printf("Strings are equal\n");
} else {
printf("Strings are not equal\n");
}
return 0;
}
Finds the first occurrence of a character in a string:
Example
#include <stdio.h>
#include <string.h>
int main() {
char str[] = "Hello, World!";
char *ptr = strchr(str, 'o');
if (ptr != NULL) {
printf("First occurrence of 'o' found at position: %ld\n", ptr - str);
} else {
printf("Character not found\n");
}
return 0;
}
#include <string.h>
int main() {
char str[] = "Hello, World!";
char *ptr = strchr(str, 'o');
if (ptr != NULL) {
printf("First occurrence of 'o' found at position: %ld\n", ptr - str);
} else {
printf("Character not found\n");
}
return 0;
}
Copying memory blocks:
Example
#include <stdio.h>
#include <string.h>
int main() {
char src[] = "Hello, World!";
char dest[50];
memcpy(dest, src, strlen(src) + 1);
printf("Copied memory: %s\n", dest);
return 0;
}
#include <string.h>
int main() {
char src[] = "Hello, World!";
char dest[50];
memcpy(dest, src, strlen(src) + 1);
printf("Copied memory: %s\n", dest);
return 0;
}
Notes
- When using string functions, ensure that the destination buffer has enough space to store the result to avoid buffer overflow.
strncpyandstrncatCan specify the maximum number of characters to copy or concatenate, which helps prevent buffer overflow.strtokThe function is not thread-safe because it internally uses static variables to save context. If used in a multithreaded environment, you need to usestrtok_rfunction.- Usage
memcpywhen ... the source and destination memory areas should not overlap. If overlap may occur, you should usememmove。
By understanding and using<string.h>The provided functions allow convenient string and memory operations, enabling more efficient and reliable C programs.