Explanation of sprintf function in C language

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srpintf() The function is very powerful ： More efficient than some string manipulation functions ; And more flexible ; You can output the desired result to the specified string , It can also be used as a buffer , and printf Can only be output to the command line ~

The header file ：stdio.h

The functionality ： Formatted string , Write the formatted data to the string .

The function prototype ：int sprintf(char *buffer, const char *format, [argument]…)

Parameters ：

（1）buffer： yes char Pointer to type , Pointer to the written string ;

（2）format： Formatted string , That is, the format you want in the program ;

（3）argument： Optional parameters , Can be any type of data ;

Function return value ：buffer The length of the string pointed to ;

use ：

（1） Format numeric strings ： At this point sprintf and printf In the same way , It's just that the printing location is different , The former is printed to buffer character string , The latter is printed to standard output , therefore sprintf It can also be used to convert an integer to a string , Than itoa Efficient and so simple ~ such as ：sprintf(buffer, “%d”, 123456); After execution buffer That is to point to the string “123456”~

（2） Connecting characters ：

Here are two examples to illustrate this problem ：

（a） Connect with ’\0’ Ending string ：

#include<stdio.h>  
int main()  
{  
    char buffer[10];  
    char *a = "1234";  
    char *b = "5678";  
    sprintf(buffer, "%s%s", a, b);  
    printf("%s\n", buffer);  
    return 0;  
} 

Copy

The result is 12345678.

（b） There is no... At the end of the connection ’\0’ Character array or string buffer for ：

include<stdio.h>
int main()
{
	char a[] = {'1', '2', '3', '4'};
	char b[] = {'5', '6', '7', '8'};
	char buffer[10];
	sprintf(buffer, "%.4s%.4s", a, b);
	printf("%s\n", buffer);
	return 0;
}

Copy

The result is 12345678.

（c） If we want to dynamically get the length of the character buffer to be processed , Then put the top sprintf Change it to ：sprintf(buffer, “%.*s%.*s”, sizeof(a), a, sizeof(b), b); that will do ~

（3） utilize sprintf Return value in

because sprintf The return value of the function is output+pos The length of the string pointed to , So for pos Come on , Equivalent to one execution pos+=sizeof(output+pos), If this statement is placed in a loop , Then execute... For the second time sprintf when output+pos It then points to the end of the current buffer （ Notice that it's not output At the end of ！ Otherwise, illegal memory will be read ！）, In this way, a string with certain rules can be generated ~ Write an example ：

    #include<stdio.h>
    int main()
    {
    	char buf[100];
    	int pos = 0;
    	for(int j = 0; j < 10; j++)
    		pos += sprintf(buf+pos, "%d-", j);
    	buf[pos-1] = '\n';// Put the last character '-' Convert to '\n'
    	printf(buf);
    	return 0;
    }

Copy

pos Each time 2, Because every time buf The string must be followed by two characters j and ‘-’. give the result as follows

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