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1. Strrchrchar * strrchr (const char * str, int c)

Search for the position of the last occurrence of the character c (an unsigned character) in the string pointed to by the parameter str.

Parameters.

Str-- C string.

C-the character to search for. Passed in int form and eventually converted back to char form.

Return value

This function returns the position of the last occurrence of the character c in str. If the value is not found, the function returns a null pointer.

Example # include # include int main () {int len; char str [] = "www.baidu.com"; char ch ='.'; char* ret; ret = strrchr (str, ch); printf ("string after% c is% s\ n", ch, ret); return 0;} output

2. Atoiint atoi (const char * str)

Converts the string pointed to by the parameter str to an integer (of type int).

Parameters.

Str-the string to convert to an integer.

Return value

This function returns a long converted integer or zero if no valid conversion is performed.

Example # include # include # include int main () {int val; char str [20] = "20220228"; val = atoi (str); printf ("string value =% s, integer value =% d\ n", str, val); strcpy (str, "hhhhh"); val = atoi (str); printf ("string value =% s, integer value =% d\ n", str, val) Return 0;} output

3. Strcatchar * strcat (char * dest, const char * src)

Append the string pointed by src to the end of the string pointed to by dest.

Parameters.

Dest-points to the target array, which contains a C string and is sufficient to hold the appended string.

Src-- points to the string to be appended, which does not overwrite the target string.

Return value

This function returns a pointer to the final target string dest.

Example # include # include int main () {char src [50] = "This is source", dest [50] = "This is destination"; strcat (src, dest); printf ("% s", src); return 0;} output

4. Strstrchar * strstr (const char * str1, const char * str2)

Used to determine whether the string str2 is a substring of str1. If so, the function returns the address where str2 first appeared in str1; otherwise, it returns NULL.

Parameters.

The C string of the str1-- to be retrieved.

The small string that str2-- searches for within the haystack string.

Return value

This function returns the location where the str2 string first appeared in str1, or null if it is not found.

Example # include # include int main () {char str1 [20] = "www.baidu.com"; char str2 [10] = ".baidu"; char* ret; ret = strstr (str1, str2); printf ("% s", ret); return (0);} output

Strncasecmpint strncasecmp (const char * S1, const char * S2, size_t n)

Function under Linux, comparing the first n characters of arguments S1 and S2 strings, and ignoring character case

Parameters.

S1: string 1

S2: string 2

Len: maximum number of characters compared

Return value

Return 0 if S1 and S2 match (equal); return a value greater than 0 if S1 is greater than S2; return a value less than 0 if S1 is less than S2

6. Strncpychar * strncpy (char * dest, const char * src, size_t n)

Copy the string pointed by src to dest, with a maximum of n characters. When the length of the src is less than n, the rest of the dest is filled with empty bytes.

Parameters.

Dest-points to the target array used to store the replicated content.

Src-- the string to copy.

N-the number of characters to copy from the source.

Return value

This function returns the final copied string.

Example # include # include int main () {char src [40] = "i am src hh."; char dest [12]; memset (dest,'\ 0mm, sizeof (dest)); strncpy (dest, src, 10); printf ("% s\ n", dest); return 0;} output

7. Strcspnsize_t strcspn (const char * str1, const char * str2)

The retrieval string str1 begins with several consecutive characters that do not contain characters in the string str2.

Parameters.

Str1-the C string to be retrieved.

Str2-- this string contains a list of characters to match in str1.

Return value

This function returns the number of characters with no characters in the string str2 at the beginning of the str1.

Example: # include # include int main () {int len; char str1 [] = "www.baidu.com"; char str2 [] = "bc"; len = strcspn (str1, str2); printf ("first matching character in% d", len); return (0);} output

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