Summary of c language fprintf, fscanf, sscanf and sprintf function knowledge points

fprintf:

fprintf() works the same as printf().printf prints output to the terminal screen, fprintf prints output to a file.
The return value of fprintf() is the number of characters output, or a negative value if an error occurs.

fprintf(fp,"arr[%d]=%d\n",i,arr[i]);//Print the written result tooutput in the specified file

void fprintf_tset(void){FILE *fp;fp=fopen("fprintf_tset.txt","w");//Open the file by writingint arr[]={1,2,3,4,5};for(int i=0;i<5;i++){fprintf(fp,"arr[%d]=%d\n",i,arr[i]);//Print the written result to the specified file for output}fclose(fp);//Close the file}

sprintf:

sprintf is a variadic function defined as follows:

int sprintf( char *buffer, const char *format [, argument] ... );

Function function: write formatted data to a string
Function prototype: int sprintf( char *buffer, const char *format [, argument] … );
Return value: string length(strlen)

void sprintf_tset(void){char str[100];char str01[10]="135245";sprintf(str,"%s",str01);printf("%s",str);}

For example, in the above piece of code, store a formatted string in the array of str01, and then use the sprintf function to assign and write the str string, and then print it.

fscanf:

The header file of the fscanf() function is , and the function prototype is int fscanf(FILE*stream, constchar*format, [argument...]);

Its function is to write data (argument) from the input stream (stream) according to the data format (format).

[Parameter] stream is the file pointer, format is the format string, and argument is the parameter corresponding to the format control character.

From the file pointed to by the file pointer fp, the data is read in the corresponding control format in format and stored in the variable corresponding to agars.

void fscanf_tset(void){FILE *fp;fp=fopen("fscanf_tset.txt","r");//The way to open the file is to readint arr[10];//Define a character array to storeif(NULL==fp){printf("No such file!");//Judgment}else{fscanf(fp,"%d ",&arr[0]);//The element value assigned to the character array}printf("%d",arr[0]);//Print the output in the terminalfclose(fp);//Close the file}

sscanf:

The role of sscanf: from a String reads data that matches the specified format.It can be used to extract integers, floating-point numbers and strings from strings.

The difference between sscanf and scanf: scanf takes the keyboard as the input source, and sscanf takes the string as the input source.

void sscanf_tset(void){char str[100];char str01[10]="1352465";sscanf("12345","%s",str);sscanf(str01,"%s",str);printf("%s",str);}

Homework exercise:

Read two strings of characters from two different files, merge the two strings, sort them alphabetically, and write them into a third file.

#include #include void fprintf_r(void){FILE *fp01;char ch01[100];char arr[100];fp01 = fopen("fprintf_r_01.txt","r");if(NULL==fp01){printf("No such file");}else{fgets(ch01,40,fp01);}printf("fprintf_r_01.txt file content is: %s\n",ch01);FILE *fp02;char ch02[100];fp02 = fopen("fprintf_r_02.txt","r");if(NULL==fp01){printf("No such file");}else{fgets(ch02,40,fp02);}printf("fprintf_r_01.txt file content is: %s\n",ch02);char str[20];sprintf(str,"%s%s",ch01,ch02);//Core: write two strings directly, write formatted data into a stringprintf("The content of the merged two files is: %s\n",str);char *p=str;int i,j;char temp;for(i=0;i*(p+j+1)){temp=*(p+j);*(p+j)=*(p+j+1);*(p+j+1)=temp;}}}printf("The contents of the two files after merging and sorting are: %s",str);FILE *fp03;char arr03[100];fp03 = fopen("fprintf_r_03.txt","w");fputs(str,fp03);fclose(fp03);}int main(){fprintf_r();return 0;} 

Analysis of key points:

The difficulty of this question is how to merge after obtaining two strings of characters. At this time, we cleverly used the sprintf() function:

Core: Write two strings directly to write formatted data into a string

sprintf(str,"%s%s",ch01,ch02);span>

The rest is relatively simple, and then use the write "w" operation to write to the specified file.