Usage of sprintf() function in C language

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sprintf Function usage

1、 This function is contained in stdio.h In the header file . 2、sprintf In peace, we often use printf The functions are very similar .sprintf Function to print to a string （ Note that the length of the string should be enough to accommodate the printed content , Otherwise, there will be a memory overflow ）, and printf Function prints out to the screen .sprintf Function is widely used in our operation of converting other data types into string types . 3、sprintf Format of function ： int sprintf( char *buffer, const char *format [, argument,…] ); Except that the first two parameters are fixed , Optional parameters can be any number of .buffer Is the character array name ;format It's a formatted string （ image ：”%3d%6.2f%#x%o”,% And # When used together , Automatically precede hexadecimal numbers with 0x）. As long as printf Format string that can be used in , stay sprintf You can use . The format string is the essence of this function . printf and sprintf Both use a formatted string to specify the format of the string , Inside the format string, use some to ”%” Format specifier at the beginning to occupy a position , Provide the corresponding variables in the following variable parameter list , In the end, the function will replace the specifier with a variable in the corresponding position , Generate a string that the caller wants . 4、 Can control the accuracy char str[20]; double f=14.309948; sprintf(str,”%6.2f”,f); 5、 You can connect multiple numerical data char str[20]; int a=20984,b=48090; sprintf(str,”%3d%6d”,a,b); str[]=”20984 48090” 6、 You can connect multiple strings into a string char str[20]; char s1[5]={‘A’,’B’,’C’}; char s2[5]={‘T’,’Y’,’x’}; sprintf(str,”%.3s%.3s”,s1,s2); %m.n In the output of the string ,m Width , The number of columns shared by strings ;n Represents the actual number of characters .%m.n In floating point numbers ,m Also means width ;n Represents the number of decimal places . 7、 You can dynamically specify , The number of characters to be intercepted char str[20]; char s1[5]={‘A’,’B’,’C’}; char s2[5]={‘T’,’Y’,’x’}; sprintf(str,”%.*s%.*s”,2,s1,3,s2); sprintf(str, “%*.*f”, 10, 2, 3.1415926); 8、 You can print it out i The address of char str[20]; int i; sprintf(str, “%p”, &i); The above statement is equivalent to sprintf(str, “%0*x”, 2 * sizeof(void *), &i); 9、sprintf The return value of is the number of characters in the character array , The length of the string , No need to call strlen(str) Find the length of the string . 10、 Use the string pointed by the character pointer to receive the printed content Example ：

int main()
{
    int ddd=666;
    char *buffer=NULL;    
    if((buffer = (char *)malloc(80*sizeof(char)))==NULL)
    {
        printf("malloc error\n");
    }
    sprintf(buffer, "The value of ddd = %d", ddd);//The value of ddd = 666
    printf("%s\n",buffer);
    free(buffer);
    buffer=NULL;
    return 0;
}

Copy

When the pointer was first defined , Does not point to where , Can point to a variable , And then you can use , If you want to simply use this pointer , Then give this pointer malloc Allocate a piece of memory , added malloc Just add stdlib.h 11、 Imagine when you take a record out of a database , Then you want to join their fields into a string according to some rules , You can use this method , In theory , He should be better than strcat Efficient , because strcat Each call needs to find the last string end character first ’\0 The location of , And in the example given above , We use it every time sprintf The return value records the location directly . Example ：

void main(void)
{ 
    char buffer[200], s[] = "computer", c = 'l'; 
    int i = 35, j; 
    float fp = 1.7320534f; // 
    j = sprintf( buffer, " String: %s\n", s ); // 
    j += sprintf( buffer + j, " Character: %c\n", c ); // 
    j += sprintf( buffer + j, " Integer: %d\n", i ); // 
    j += sprintf( buffer + j, " Real: %f\n", fp );// 
    printf( "Output:\n%s\ncharacter count = %d\n", buffer, j );
}

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This example is to connect all the defined data with the characters in the format control block , Finally print it out buffer And the number of characters in the string . The result is shown in the figure ：

12、 Format numeric strings sprintf One of the most common applications is to print integers into strings . Such as ： （1） Integer 123 Print it as a string and save it in s in . sprintf(s, “%d”, 123); // produce “123″ （2） You can specify the width , Fill in the blanks on the left side of the deficiency ： sprintf(s, “%8d%8d”, 123, 4567); // produce ：“ 123 4567″ Of course, it can also be left aligned ： sprintf(s, “%-8d%8d”, 123, 4567); // produce ：“123 4567″ （3） You can also follow 16 Binary printing ： sprintf(s, “%8x”, 4567); // A lowercase letter 16 Base number , Width share 8 A place , Right alignment sprintf(s, “%-8X”, 4568); // Capitalization 16 Base number , Width share 8 A place , Align left such , An integer 16 The binary string is easy to get , But we're printing 16 When the content is decimal , I usually want a left complement 0 The same width format of , What should I do ？ It's simple , Add... Before the number for width 0 That's all right. . sprintf(s, “%08X”, 4567); // produce ：“000011D7″ On top of it ”%d” On going 10 This left complement can also be used in decimal printing 0 The way . Here we should pay attention to the problem of symbol extension ： such as , If we want to print short integers （4）（short）-1 Of memory 16 The hexadecimal representation , stay Win32 On the platform , One short Type occupation 2 Bytes , So naturally we want to use 4 individual 16 Print it in decimal digits ： short si = -1; sprintf(s, “%04X”, si); produce “FFFFFFFF, What's going on? ？ because sprintf It's a variable parameter function , In addition to the first two parameters , The following parameters are not type safe , There's no way for a function to pass through just one “%X” You can know when the parameters were pressed on the stack before the function call What is being pushed in 4 An integer of bytes is still 2 Short integer in bytes , So we took a unified approach 4 How bytes are handled , The symbol extension is made when the parameter stack is pressed , Expanded to 32 An integer -1, When printing 4 It's not enough , Just put 32 An integer -1 Of 8 position 16 It's all printed out . If you want to see si As it is , So let the compiler do 0 Extension, not symbolic extension （ When expanding, the binary left complement 0 Instead of complementing the sign bit ）： sprintf(s, “%04X”, (unsigned short)si); That's all right. . perhaps ： unsigned short si = -1; sprintf(s, “%04X”, si); sprintf and printf You can also press 8 Decimal print integer string , Use ”%o”. Be careful 8 Into the system and 16 It doesn't print negative numbers , It's all signed , In fact, it is the direct use of internal coding of variables 16 Base or 8 Hexadecimal said .

Reference resources ：http://blog.csdn.net/cos_sin_tan/article/details/7548632http://nnssll.blog.51cto.com/902724/198237/http://blog.csdn.net/s202090414/article/details/8690518http://blog.csdn.net/peng___peng/article/details/51510685

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