Printf function and scanf function in C language

1. scanf、sscanf and fscanf function

1.1 scanf function

Standard input functions . The grammar is as follows ：

int scanf( const char *format, … )

By using %s Format control string completion , But you can't read in spaces 、 Line break 、 tabs (\t) So score separator . Can pass %[^%n]s Complete the reading of the string with spaces .

1.2 sscanf function

s representative string, Used to read formatted characters

// Examples of use 
sscanf("1/2/3", "%d/%d/%d", &a1, &a2, &a3)

1.3 fscanf function

f representative file, Perform formatted input from a stream

  char str_r[1000]={
    0};
  FILE *fp_r = fopen("./test.txt", "r");
  fscanf(fp_r, "%[^\n]s", str_r);
  fclose(fp_r);
  printf("%s\n", str_r);
  return 0;

2. printf、sprintf and fprintf function

2.1 prinrf function

Standard output function . The grammar is as follows ：int printf(const char *format, …)

2.2 sprintf function

The function used to format the output string

sprintf("1/2/3","%d-%d-%d", a1, a2, a3)

2.3 fprintf function

Formatted string , And output the results to the formulated documents , Know that the end of string appears (\0") until

  char str[1000]="Hello world!";
  FILE *fp = fopen("./test.txt","w");
  fprintf(fp, "%s", str);
  fclose(fp);

3. Use small examples

3.1 sscanf and sprintf

#include<stdio.h>
int main(){
    
    char str[100] = "192.168.0.1";
    int a, b, c, d;
    sscanf(str, "%d.%d.%d.%d", &a, &b, &c, &d);
    printf("a = %d, b = %d, c = %d, d = %d\n", a, b, c, d);
    sprintf(str, "%[email protected]%[email protected]%[email protected]%d\n", a, b, c, d);
    int num = printf("str=%s",str);
    printf("%d", num);
    return 0;
}

3.2 fscanf and fprintf

#include<stdio.h>
int main(){
    
    char str[1000]="Hello world!";
    char str_r[1000]={
    0};
    FILE *fp = fopen("./output","w");
    fprintf(fp, "%s", str);
    fclose(fp);
    FILE *fp_r = fopen("./output", "r");
    fscanf(fp_r, "%[^\n]s", str_r);
    fclose(fp_r);
    printf("%s\n", str_r);
    return 0;
}