String handler

gets

#include <stdio.h>
char *gets(char *s);
Function: read characters from standard input and save them to s The specified memory space until a newline occurs or the end of the file is read.
Parameters:
	s: First address of string
 Return value:
	Success: read in string
	Failed: NULL

The difference between gets and scanf

Differences between gets(str) and scanf('% s', str):

• gets(str) allows the input string to contain spaces
• scanf('% s', str) does not allow spaces

Note: because scanf() and gets() cannot know the size of string s, they must encounter a newline character or receive input until the end of the file. Therefore, it is easy to cause the character array to cross the boundary (buffer overflow).

A method that allows scanf to also receive spaces

char ch[100];
scanf("%[^\n]",ch);

routine

char str[100];
printf("Please enter str: ");
gets(str);
printf("str = %s\n", str);

puts

#include <stdio.h>
int puts(const char *s);
Function: standard equipment output s String, which is automatically output after the output is completed'\n'. 
Parameters:
	s: First address of string
 Return value:
	Success: non negative
	Failed:-1

Compared with printf, puts will automatically output a '\ n' after the output is completed

routine

#include <stdio.h>

int main()
{
	printf("hello world");
	puts("hello world");

	return 0;
}

printf does not add \ n does not print line breaks, and puts will automatically output one after the output is completed \ n

fgets

#include <stdio.h>
char *fgets(char *s, int size, FILE *stream);
Function: from stream Read in characters from the specified file and save to s The specified memory space until a newline character appears, the end of the file is read, or has been read size - 1 Characters will be added automatically at the end '\0' Ends as a string.
Parameters:
	s: character string
	size: Specifies the length of the maximum read string( size - 1)
	stream: File pointer. If you read the string entered by the keyboard, write it as stdin
 Return value:
	Success: String successfully read
	End of file read or error: NULL

When fgets() reads a string entered by the user through the keyboard, it also takes the carriage return entered by the user as a part of the string. When inputting a string through scanf and gets, it does not contain the ending "\ n", but there is more "\ n" at the end through fgets. The fgets() function is safe and there is no buffer overflow problem.

routine

#include <stdio.h>

int main()
{
	char str[100];
	printf("Please enter str: ");
	fgets(str, sizeof(str), stdin);
	printf("str = \"%s\"\n", str);
	return 0;
}

fputs

#include <stdio.h>
int fputs(const char * str, FILE * stream);
Function: will str Writes the specified string to stream String terminator in the specified file '\0'  Do not write to file. 
Parameters:
	str: character string
	stream: File pointer. If the string is output to the screen, it is fixed as stdout
 Return value:
	Success: 0
	Failed:-1

Fputs() is the file operation version of puts(), but fputs() will not automatically output a '\ n'

routine

#include <stdio.h>

int main()
{
	printf("hello world");
	puts("hello world");
	fputs("hello world", stdout);
	return 0;
}
 

strlen

#include <string.h>
size_t strlen(const char *s);
Function: calculate the specified string s The length of the string, excluding the string terminator'\0'
Parameters:
s: First address of string
 Return value: String s The length of the, size_t by unsigned int type

be careful:
① Does not contain string terminator '\ 0'
② Need to import library

strcpy

#include <string.h>
char *strcpy(char *dest, const char *src);
Function: handle src Copy the string pointed to to to dest In the space pointed to,'\0'It will also be copied
 Parameters:
	dest: Destination string first address
	src: Source character prefix address
 Return value:
	Success: Return dest First address of string
	Failed: NULL

Note: if the memory space referred to by the parameter dest is not large enough, it may cause a buffer overflow error.

strncpy

#include <string.h>
char *strncpy(char *dest, const char *src, size_t n);
Function: handle src Points to the front of the string n Characters copied to dest In the space pointed to, whether to copy the terminator depends on whether the specified length contains'\0'. 
Parameters:
	dest: Destination string first address
	src: Source character prefix address
	n: Specifies the number of strings to copy
 Return value:
	Success: Return dest First address of string
	Failed: NULL

strcpy and strncpy

#include <stdio.h>
#include <stdlib.h>

int main()
{
	char a[10] = "hello";
	char b[10];
	char c[10];
	strcpy(b,a);
	strncpy(c,a,5);

	printf("%s\n",a);
	printf("%s\n",b);
	printf("%s\n",c);

	return 0;
}

strncpy will not automatically copy '\ 0'

strcat

#include <string.h>
char *strcat(char *dest, const char *src);
Function: will src Connect string to dest The tail of the,'\0'Will also add the past
 Parameters:
	dest: Destination string first address
	src: Source character prefix address
 Return value:
	Success: Return dest First address of string
	Failed: NULL

strncat

#include <string.h>
char *strncat(char *dest, const char *src, size_t n);
Function: will src Before string n Characters connected to dest The tail of the,'\0'Will also add the past
 Parameters:
	dest: Destination string first address
	src: Source character prefix address
	n: Specifies the number of strings to append
 Return value:
	Success: Return dest First address of string
	Failed: NULL

Note:
① The appended target string needs enough space
② In append, the \ 0 in the target string is removed first, and then the \ 0 in the source string is appended
③ Limited append note: limited append will also append \ 0

strcmp

#include <string.h>
int strcmp(const char *s1, const char *s2);
Function: comparison s1 and s2 Character size, yes ASCII Code size.
Parameters:
	s1: First address of string 1
	s2: First address of string 2
 Return value:
	Equal: 0
	Greater than:>0
	Less than:<0

strncmp

#include <string.h>
int strncmp(const char *s1, const char *s2, size_t n);
Function: comparison s1 and s2 front n The size of characters, compared with characters ASCII Code size.
Parameters:
	s1: First address of string 1
	s2: First address of string 2
	n: Compares the specified number of strings
 Return value:
	Equal: 0
	Greater than: > 0
	Less than: < 0

sprintf

#include <stdio.h>
int sprintf(char *_CRT_SECURE_NO_WARNINGS, const char *format, ...);
Function: according to parameters format String to convert and format the data, and then output the result to str In the specified space until the string terminator appears '\0'  until.
Parameters:
	str: First address of string
	format: String format, usage and printf()equally
 Return value:
	Success: number of characters actually formatted
	Failed: - 1

sscanf

#include <stdio.h>
int sscanf(const char *str, const char *format, ...);
Function: from str Reads the data according to the specified string and reads the data according to the parameters format String to convert and format data.
Parameters:
	str: The first address of the specified string
	format: String format, usage and scanf()equally
 Return value:
	Success: number of parameters, number of successfully converted values
	Failed: - 1

be careful:
① Like scanf, sscanf needs to add warnings at the beginning of the program
② Return the specific number upon success. Failure - 1

strchr

#include <string.h>
char *strchr(const char *s, int c);
Function: in string s Find letters in c Location of occurrence
 Parameters:
	s: First address of string
	c: Match letters(character)
Return value:
	Success: returns the first occurrence c address
	Failed: NULL

strstr

#include <string.h>
char *strstr(const char *haystack, const char *needle);
Function: in string haystack Find string in needle Location of occurrence
 Parameters:
	haystack: First address of source string
	needle: First address of matching string
 Return value:
	Success: returns the first occurrence needle address
	Failed: NULL

strtok

#include <string.h>
char *strtok(char *str, const char *delim);
Function: to divide the string into fragments. When strtok()In parameter s Parameter found in string delim When dividing characters contained in, The character is changed to\0 Character. When multiple characters appear in succession, only the first one is replaced with\0. 
Parameters:
	str: Point to the string to be split
	delim: Splits all characters contained in the string
 Return value:
	Success: the first address of the split string
	Failed: NULL

• On the first call: strtok() must give the parameter s string
• In subsequent calls, the parameter s is set to NULL, and each successful call returns a pointer to the segmented fragment

be careful:
① The cutting point is represented by \ 0. After cutting, the original string style will be destroyed
② When multiple split characters appear in succession, only the first one is replaced with \ 0

atoi

#include <stdlib.h>
int atoi(const char *nptr);
Function: atoi()Can scan nptr String, skip the preceding space character, and do not start the conversion until it encounters a number or sign, but encounter a non number or string terminator('\0')To end the conversion and return the result to the return value.
Parameters:
	nptr: String to be converted
 Return value: integer after successful conversion

• atof(): converts a decimal string into a floating-point number.
• atol(): converts a string to a long type

Note: ① skip the preceding space character, and do not start the conversion until you encounter a number or sign, while do not end the conversion until you encounter a non number or string Terminator ('\ 0')