Summary of several common functions of C language strings

String processing functions

1. Write formatted data into a string: sprintf

Int sprintf (char * buffer, const char * format ,...);

Print data to buffer

Example: char result [100];

Int num = 24;

Sprintf (result, "% d", num );

Example: char string [50];

Int file_number = 0;

Sprintf (string, "file. % d", file_number );

File_number ++;

Output_file = fopen (string, "w ");

For example, char result [100];

Float fnum = 3.14159;

Sprintf (result, "% f", fnum );

2 String Length query function: strlen

Int strlen (const char * s );

3. String replication functions: strcpy and strncpy

Char * strcpy (char * dest, const char * src );

4. String concatenation function: strcat

Char * strcat (char * dest, const char * src );

5. String comparison functions: strcmp, strncmp, stricmp, and strnicmp

String comparison function strcmp (case sensitive)

Int strcmp (const char * s1, const char * s2 );

Return Value

Return value

Explanation

Less than 0

Str1 is less than str2

Equal to 0

Str1 is equal to str2

Greater than 0

Str1 is greater than str2

String search functions: strcspns, strspns, strstr, strtok, strchr

6. Search for the substring strstr.

Char * strstr (char * s1, char * s2 );

Returns the position pointer for the first occurrence of a given string.

If this parameter is found, a pointer is returned, pointing to the position where s2 appears for the first time in s1.

If no value is found, NULL is returned.

Pdest = strstr (string, str );

Search for 'str' in 'string' and return the position where 'str' appears for the first time in 'string '.

For example: char * str1 = "this is a string of characters ";

Char * str2 = "a string ";

Char * result = strstr (str1, str2 );

If (result = NULL) printf ("cocould not find % s in % s", str2, str1 );

Else printf ("Found a substring: % s", result );

Output result: Found a substring: a string of characters

7. Search for the position strchr where the character first appears in the string

Pdest = strchr (string, ch );

Search for ch in string and return the position where str appears for the first time in string.

8. Copy strncpy from the string, and copy all strcpy from the string.

Char * strncpy (char * dest, char * src, int maxlen );

Char * strcpy (char * dest, char * src );

Copy the previous maxlen characters from src to dest

1) if the src contains less than maxlen characters, it will be copied together ''.

2) If src contains more than or equal to maxlen characters, copy maxlen characters

9 string case-insensitive conversion functions: strlwr, strupr

Supplement: These functions require # include <string. h>