How to get exclude null terminators when reading in a string? - c

This program opens a file that contains a lake's name and its volume in units of hundreds of cubic miles--separated by a space. Its output is supposed to be the lake's name followed by a number of asterisks to represent its volume to the nearest hundred cubic mile (for example, a lake that has 12.7 hundred cubic miles in volume would print 13 asterisks). However, when it reads in a name that contains a space, it reads up until the space and then prints the next string in a new line. Is there any way I can read "gross dirty lake" as one line instead of "gross\ndirty\nlake" for example? Here's what I have so far:
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
void name_asterisks(char name[20], float vol);
main() {
FILE *fp;
fp = fopen("lakes.txt", "r");
char name[20];
float vol;
if (fp == NULL) {
printf("File does not exist.\n");
system("pause");
return 0;
}
while (fscanf(fp, "%s %f", name, &vol) != EOF) {
name_asterisks(name, vol);
}
fclose(fp);
system("pause");
}
void name_asterisks(char name[20], float vol) {
int i;
printf("%s", name);
for (i = 0; i < (int)roundf(vol); i++)
printf("*");
printf("\n");
}

"%s" is for scanning non-white-space. Code needs a different format specifier.
char buf[100];
while (fgets(buf, sizeof buf, fp) != NULL) {
if (sscanf(buf, " %19[A-Za-z ]%f", name, &vol) != 2) {
fprintf(stderr, "Unexpected data\n");
break;
}
name_asterisks(name, vol);
}
" ": Skip white-spaces.
"%19[A-Za-z ]": Scan and save up to 19 letters or spaces, append '\0'.
"%f": Skip white-spaces and save scan a float.
Note about original code: Better to check for what code wants than checking against 1 undesired result
// while (fscanf(fp, "%s %f", name, &vol) != EOF) {
while (fscanf(fp, "%s %f", name, &vol) == 2) {

sample for like as gross dirty lake 12.7\n
#include <string.h> //for strrchr
...
char line[64];//line buffer
...
while (fgets(line, sizeof line, fp)){
char *p = strrchr(line, ' ');//search last ' '
*p = '\0';
//snprintf(name, sizeof(name), "%s", line);
vol = atof(p+1);
name_asterisks(line, vol);//name_asterisks(name, vol);
}

Related

write file to structs

I want to write and read some statics from file to structs.
write from structs to file is work of but write data from file isn't ok.
I will be grateful to help me what is the problem.
#include <stdio.h>
#include <stdlib.h>
const char* MemberFormatIn="(%[^,], %[^,], %[^,], %d)";
const char* MemberFormatOut="(%s, %s, %s, %d)\n";
typedef struct member {
char name[20],
lastName[20],
address[20];
int age;
}p1,p2;
void inputMemberList(struct member p[],int count) {
printf("name:");
scanf("%s",p[count].name);
printf("lastName:");
scanf("%s",p[count].lastName);
printf("address:");
scanf("%s",p[count].address);
printf("age:");
scanf("%d",&p[count].age);
}
void printMemberList(struct member p[],int count) {
system("cls");
for(int i=0; i<count; i++) {
printf("\aMember %d:\n", i+1);
printf("Name is: %s", p[i].name);
printf("\nLast name is: %s", p[i].lastName);
printf("\nAddress is: %s", p[i].address);
printf("\nAge is: %d", p[i].age);
printf("\n\n");
}
}
void saveMember(struct member p[],int count) {
FILE* fp = fopen("member.txt","a+");
if (fp == NULL) {
printf("File can't open.");
exit(1);
}
fprintf(fp, MemberFormatOut, p[count].name, p[count].lastName, p[count].address, p[count].age);
fclose(fp);
}
void fileToStructure(struct member p[],int count) {
FILE* fp = fopen("member.txt","a+");
if (fp == NULL) {
printf("File can't open.");
exit(1);
}
fseek(fp, 0, SEEK_SET);
for (int i=0; i<count+1; i++) {
fscanf(fp, MemberFormatIn, p[i].name, p[i].lastName, p[i].address, &p[i].age);
}
fclose(fp);
}
int numberOfMember() {
int count = 0;
char c;
FILE* fp = fopen("member.txt","r");
if(fp == NULL) {
printf("File can't open.");
exit(1);
}
do {
c = fgetc(fp);
if(c == '\n')
count++;
}while(c != EOF);
fclose(fp);
return count;
}
int main() {
int len = 100;
p1 p[len];
int count = numberOfMember();
inputMemberList(p,count);
saveMember(p,count);
fileToStructure(p,count);
printMemberList(p,count);
return 0;
}
at result just statics of member true and shown show but the others doesn't true.
File data(example):
(ahmad, dad, tir, 12)
(hossein, dad, tiran, 12)
(ali, dad, tir, 15)
(mohammadi, mmad, tiron, 16)
(helma, dad, tiran, 5)
(mohammad, amin, dadkhah, 5)
output(example):
Member 1:
Name is: ahmad
Last name is: dad
Address is: tir
Age is: 12
Member 2:
Name is: ├wöΩ\`
Last name is:
Address is: ↑
Age is: 0
Member 3:
Name is: Ä
Last name is: t
Address is: e
Age is: 7471221
Member 4:
Name is: r
Last name is: l
Address is: o
Age is: 6881396
Member 5:
Name is: n
Last name is: s
Address is:
Age is: 0
Member 6:
Name is:
Last name is:
Address is:
Age is: 0
In fileToStructure(), the first iteration of the loop calls fscanf() and if all is OK, the next character to be read from the file will be the newline character at the end of the first line. Unfortunately for the next iteration, the next call to fscanf() is expecting to read the ( character, but instead it reads the newline character. This will cause this call to fscanf() and all the subsequent calls to fail to match anything and return EOF.
The code needs to eat the newline character. One way to do that is to change the MemberFormatIn format string to one of the following:
const char* MemberFormatIn=" (%[^,], %[^,], %[^,], %d)"; - will discard any whitespace characters before the ( character; or
const char* MemberFormatIn="(%[^,], %[^,], %[^,], %d) "; - will discard any whitespace characters after the ) character.
The first one (discarding whitespace before the ( character) would be preferable for interactive input, but it doesn't matter too much when reading from a file.

For loop doesn`t work when add [^\n] to a scanf_s

This program should ask you to add member (people) to a struct and print them on a file but after the first for loop just stop working and jump over the name part. I just found that thing that allow you to add space to a string, tried it but no success...
I tried to remove it and it work without any problem so the [^\n] make something go wrong.
What is wrong ?
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
struct Staff {
char Surname[100];
char Name[100];
int age;
char spec[100];
int id;
} person;
void write();
void leggi();
void trova();
int main() {
write();
}
void write() {
int i = 0;
int n = 1;
int r;
FILE *fp;
fopen_s(&fp, "index.txt", "w+");
if (fp == NULL) {
printf("Failed to open file\n");
exit(1);
}
fprintf(fp, "%d\n", i);
for (i = 0; i < n; i++) {
printf("Surame:\n");
scanf_s("%[^\n]s", person.Surname, 100);
fprintf(fp, "%s\t\t", person.Surname);
//loop just get over the name part
printf("Name:\n"); //after the first loop
scanf_s("%s", person.Name, 100);
fprintf(fp, "%s\t", person.Name);
printf("Age:\n");
scanf_s("%d", &person.age);
fprintf(fp, "%d\t", person.age);
printf("Specialization\n");
scanf_s("%s", person.spec, 100);
fprintf(fp, "%s\n", person.spec);
printf("Want to enter another? 1=yes 0=no...\n");
scanf_s("%d", &r);
if (r == 1)
n = n + 1;
}
rewind(fp);
fprintf(fp, "%d\n", i);
fclose(fp);
}
There are multiple problems in your code:
you use the so called secure functions fopen_s, scanf_s etc, but you do not check the return values to detect invalid input. You should instead use standard functions, pass the appropriate arguments and check the return values.
using scanf_s is actually non portable: the scanf_s function defined in Annex K of the C Standard requires the length argument after the pointer to have size_t type, whereas the function with the same name in the Microsoft library uses type UINT, which has a different representation on 64-bit versions of their Windows OS. A classical case of the Embrace, enhance and extinguish strategy. In Standard C, one should write: scanf_s("%s", person.Name, (size_t)100) or better:
scanf_s("%s", person.Name, sizeof person.Name)
there is no need to open the output file for update with "w+", just use "w".
you rewind the stream pointer back to the beginning of file and overwrite the number of entries at the start of the file. This works as long as you have less than 10 entries, but beyond that, the number has more digits so some characters in the file will be corrupted. You could use a format with padding such as "%6d\n" which would allow for up to 1 million records without risks.
"%[^\n]s" is not a correct scanf format: you should just write "%[^\n]" or better " %99[^\n]" to skip initial white space and limit the input to 99 characters.
Here is a modified version:
#ifdef _MSC_VER
#define _CRT_SECURE_NO_WARNINGS
#endif
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
struct Staff {
char Surname[100];
char Name[100];
int age;
char spec[100];
int id;
};
void write(void);
void leggi(void);
void trova(void);
int main() {
write();
}
int flush_input(void) {
int c;
while ((c = getchar()) != EOF && c != '\n')
continue;
return c;
}
void write(void) {
int n = 0;
int r;
FILE *fp = fopen("index.txt", "w");
if (fp == NULL) {
fprintf("Failed to open file index.txt: %s\n",
strerror(errno));
exit(1);
}
fprintf(fp, "%6d\n", n);
for (;;) {
struct Staff person = { 0 };
printf("Surname:\n");
if (scanf(" %99[^\n]", person.Surname) != 1)
break;
flush_input();
fprintf(fp, "%s\t\t", person.Surname);
//loop just get over the name part
printf("Name:\n"); //after the first loop
scanf(" %99[^\n]", person.Name);
flush_input();
fprintf(fp, "%s\t", person.Name);
printf("Age:\n");
scanf("%d", &person.age);
flush_input();
fprintf(fp, "%d\t", person.age);
printf("Specialization\n");
scanf(" %99[^\n]", person.spec, 100);
flush_input();
fprintf(fp, "%s\n", person.spec);
n++;
printf("Want to enter another? 1=yes 0=no...\n");
if (scanf("%d", &r) != 1 || r != 1) {
flush_input();
break;
}
flush_input();
}
rewind(fp);
// update the entry count on 6 characters
fprintf(fp, "%6d\n", n);
fclose(fp);
}
Change the call of scanf below for entering strings by inserting a space in the beginning of the format string. For example instead of this call
scanf_s("%[^\n]s", person.Surname, 100);
(where the letter s must be removed from the format string) write
scanf_s(" %[^\n]", person.Surname, ( rsize_t )100);
^^^^^^^^
This allows to skip leading white space characters in the input buffer.
Pay attention to that changing the condition or the for loop the was as you are doing
for (i = 0; i < n; i++) {
//...
if (r == 1)
n = n + 1;
}
makes the code unclear. Instead of the for loop you could use do-while loop.

How to write, read and delete a file in a single script in C programming

I created a file and filled it with some entries. However, I want to read this file and show it on the screen. Also, after showing the entries, I want it to be deleted with my permission. But I am stuck at this point please help me.
EDIT: Code is updated but still couldn't figure it out how to do :/
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
char name[20], surname[20], city[30], country[30], gender[15];
int count = 0;
int main() {
FILE *f1;
f1 = fopen("C:\\FurkanArslan.txt", "r+");
while (count < 10) { // every step provides 5 new data, so 5*10 will provide 50 data in total.
printf("\n*Please enter required information: \n");
printf("Name :"); scanf("%s", name);
printf("Surname:"); scanf("%s", surname);
printf("Country:"); scanf("%s", country);
printf("City :"); scanf("%s", city);
printf("Gender :"); scanf("%s", gender);
fprintf(f1, " %s | %s | %s | %s | %s\n\n", name, surname, gender, city, country);
count++;
}
fclose(f1);
printf("\n<<<<<%d data has been successfully saved!>>>> \n", count * 5);
printf("-------------------------------------\n");
f1 = fopen("C:\\FurkanArslan.txt", "r");
char c, answer;
while ((c = fgetc(f1)) != EOF)
putchar(c); // In this part I displayed file on the screen.
printf("\n\n <<<< %d entries are displayed on the screen! >>>>", count * 5);
printf("\n\nWould you like to remove your file [Y/N] ?");
scanf(" %c", &answer);
if (answer == 'y' || answer == 'Y') {
remove("f1");
printf("\n\n***File successfully removed!");
}
return 0;
}
In order to show the content of a file you have to open it and read it letter by letter, after that, you can use the putchar function to output the current character
FILE *fp = fopen("path/to/file.txt","r");
char c;
while((c=fgetc(fp))!=EOF)
putchar(c);
fclose(fp);
after that to remove a file you need to use the remove function, which receives the name of the file as paramter.
remove("my_file.txt");
There are multiple issues in your code:
there is no need to make the variables and arrays global, just define them in the body of the main() function.
you should tell scanf() the maximum number of characters to store in the destination array with a length specifier in the format string (eg: "%19s") and check for conversion success.
the variable c used in the reading loop must have type int for proper detection of EOF. fgetc() returns a positive byte value if successful and the special negative value EOF at end of file.
you do not need to reopen the file after writing to it. Sine you opened it for update mode, you can just seek back to the beginning of the file with rewind(f1) or fseek(f1, 0L, SEEK_SET).
the file is open for read and update mode ("r+"): it will fail if the file does not exist. You should open it in write and update mode with "w+" to create or truncate it.
you should check that fopen succeeds at opening the file, otherwise you invoke undefined behavior passing a null stream pointer to fprintf.
to remove the file, remove() takes the filename as its argument. You must close the file before attempting to remove it.
Here is a modified version:
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main() {
const char *filename = "C:\\FurkanArslan.txt";
char name[20], surname[20], city[30], country[30], gender[15];
int count = 0;
FILE *f1 = fopen(filename, "w+");
if (f1 == NULL) {
printf("Cannot open file %s.\n", filename);
return 1;
}
while (count < 10) { // every step provides 5 new data, so 5*10 will provide 50 data in total.
printf("\n*Please enter required information: \n");
printf("Name :"); if (scanf("%19s", name) != 1) break;
printf("Surname:"); if (scanf("%19s", surname) != 1) break;
printf("Country:"); if (scanf("%29s", country) != 1) break;
printf("City :"); if (scanf("%29s", city) != 1) break;
printf("Gender :"); if (scanf("%14s", gender) != 1) break;
fprintf(f1, " %s | %s | %s | %s | %s\n\n", name, surname, gender, city, country);
count++;
}
printf("\n<<<<< %d data has been successfully saved to %s! >>>>\n",
count * 5, filename);
printf("-------------------------------------\n");
rewind(f1);
int c;
while ((c = fgetc(f1)) != EOF)
putchar(c);
printf("\n\n <<<< %d entries are displayed on the screen! >>>>\n", count);
fclose(f1);
printf("\nWould you like to remove your file [Y/N] ?");
char answer;
if (scanf(" %c", &answer) == 1 && (answer == 'y' || answer == 'Y')) {
if (remove(filename)) {
printf("\n\n***Error removing file %s: %s\n",
filename, strerror(errno));
} else {
printf("\n\n***File %s successfully removed!\n", filename);
}
}
return 0;
}

Search and write data from one file to another

I need to write a C program to fetch data from one file and write it to another file, without using user defined functions. My requirements are to:
Search customer details by Name.
Store the transaction data (paid amount) in another text file.
I did the code to search by name. But its not working,
#include <stdio.h>
#include <stdlib.h>
int main () {
char name[10], nic[10], mobile[10];
char fname[10], fnic[10], fmobile[10];
char choice;
int amount;
FILE *cfptr;
printf("Enter search type - \n 1. NAME \n 2. NIC \n 3.MOBILE \n ----> ");
scanf("%c", &choice);
printf("Enter search text : ");
scanf("%s", &name);
cfptr = fopen ("customer.dat", "r");
while (!feof(cfptr)){
fscanf(cfptr, "%s %s %s", fname, fnic, fmobile);
printf("Read Name |%s|\n", fname );
printf("Read NIC |%s|\n", fnic );
printf("Read Mobile |%s|\n", fmobile );
}
fclose(cfptr);
scanf("%d", &amount);
return(0);
}
customer.dat File
Shan 100012 200202
Marsh 121213 667675
Kim 126573 663412
This code is not complete asI cant filter the single name assigning
if(name == fname)
as am getting
assignment to expression with array type error
Can any one complete me the code to search and save to another file so I can do the amount calculation part?
int Search_in_File(char *fname, char *str) {
FILE *fp;
int line_num = 1;
int find_result = 0;
char temp[512];
//gcc users
//if((fp = fopen(fname, "r")) == NULL) {
// return(-1);
//}
//Visual Studio users
if((fopen_s(&fp, fname, "r")) != NULL) {
return(-1);
}
while(fgets(temp, 512, fp) != NULL) {
if((strstr(temp, str)) != NULL) {
printf("A match found on line: %d\n", line_num);
printf("\n%s\n", temp);
find_result++;
}
line_num++;
}
if(find_result == 0) {
printf("\nSorry, couldn't find a match.\n");
}
//Close the file if still open.
if(fp) {
fclose(fp);
}
return(0);
}
few comments:
when scanning the choice, read it as an integer and not as a character.
scanf("%c", &choice); // change to scanf("%d", &choice);
single '=' is an assigment, you meant comparison which is double '=='
if(name = fname) // comparison is if(name == fname)
in order to compare string, do not use '==' operator. use strcmp or implement an equivalent of strcmp.
Thanks for the effort, As with changes, I have changed my code as below and its working. Without checking with the name, I alternately checked with the nic.
#include <stdio.h>
int main(void){
int nic, n, mobile;
char name[30];
FILE *aPtr;
aPtr = fopen("Details.txt","w");
if(aPtr == NULL){
printf("File cannot be opened");
return -1;
}
printf("Enter nic to search - ");
scanf("%d", &n);
fscanf(aPtr, "%d %-s %d", &nic, name, &mobile);
while(!feof(aPtr)){
if(nic == n){
Printf("%d %s %d \n", nic, name, mobile);
}
fscanf(aPtr, "%d %s %d", &nic, name, &mobile);
}
fclose(aPtr);
return 0;
}

Reading and writing binary files in C

These are 2 separate applications.
In the first one, I tried to store employee details like name, age and salary in the binary file named emp.bin.
In the second application, I tried to view the contents of the file but in place of the name, only the first character appears.
I tried printing each character separately, and it turns out that there's 3 null characters '\n' after each letter in the name that is why it is not printing after the first character.
"Write" application code:
//Receives records from keyboard and writes them to a file in binary mode
#include <stdio.h>
int main()
{
FILE *fp;
char another = 'Y';
struct emp
{
char name[40];
int age;
float bs;
};
struct emp e;
fp = fopen("emp.bin", "wb");
if (fp == NULL)
{
puts("Cannot open the file.");
return 1;
}
while(another == 'Y')
{
printf("Enter the employee name, age and salary: ");
scanf("%S %d %f", e.name, &e.age, &e.bs);
while(getchar() != '\n');
fwrite(&e, sizeof(e), 1, fp);
printf("Add another record? (Y/N)");
another = getchar();
}
fclose(fp);
return 0;
}
"Read" application code:
//Read records from binary file and displays them on VDU
#include <stdio.h>
#include <ctype.h>
int main()
{
FILE *fp;
struct emp
{
char name[40];
int age;
float bs;
} e;
fp = fopen("emp.bin", "rb");
if (fp == NULL)
{
puts("Cannot open the file.");
return 1;
}
while (fread(&e, sizeof(e), 1, fp) == 1)
{
printf("\n%s \t %d \t $%.2f\n", e.name, e.age, e.bs);
}
fclose(fp);
}
Here's the input and output:
How can I correct this code to make it print the whole name?
The problem is in the "writer" application, even before the actual write is performed.
When you get data from the user
scanf("%S %d %f", e.name, &e.age, &e.bs);
you use format %S (capital letter "S". Format specifiers are case sensitive!). As we can read in the printf man page
S
(Not in C99, but in SUSv2.) Synonym for ls. Don't use.
this leads us to %ls format specifier that is described in the following way
s
[...] If an l modifier is present: The const wchar_t * argument is expected to be a pointer to an array of wide characters. Wide characters from the array are converted to multibyte characters
Talking about Windows source we have:
S
Opposite-size character string, up to first white-space character (space, tab or newline). [...]
When used with scanf functions, signifies wide-character array; when used with wscanf functions, signifies single-byte-character array [...]
So, basically, you are reading characters from stdin and converting them to wide chars. In this case every character takes sizeof(wchar_t). Probably in your system this size is 4.
What you need is simply %s format specifier. And since your name array has size 40, I suggest using
scanf("%39s", e.name );
to get the name from user. In this way up to 39 characters will be written, being the 40th reserved to the string terminator '\0'.
As noted by Roberto in his answer, the problem is the %S conversion specifier, which is a typo, you should use %s.
Note however that there are other issues which might pose problems:
you should tell scanf() the maximum number of characters to read for the employee name, otherwise scanf() may write beyond the end of the destination array if input is too long.
if both programs run on separate systems with different endianness, the numbers will be incorrect on the receiving end because their bytes will be stored in the opposite order. For this reason, endianness should be specified and handled explicitly in binary files. Text format tends to be preferred for data transmission.
Here is a modified version:
//Receives records from keyboard and writes them to a file in binary mode
#include <stdio.h>
int main() {
FILE *fp;
char another = 'Y';
struct emp {
char name[40];
int age;
float bs;
} e;
int c;
fp = fopen("emp.bin", "wb");
if (fp == NULL) {
puts("Cannot open the file.");
return 1;
}
while (another == 'Y') {
printf("Enter the employee name, age and salary: ");
if (scanf("%39s %d %f", e.name, &e.age, &e.bs) != 3)
break;
while ((c = getchar()) != EOF && c != '\n')
continue;
if (fwrite(&e, sizeof(e), 1, fp) != 1)
break;
printf("Add another record? (Y/N)");
another = getchar();
}
fclose(fp);
return 0;
}
"Read" application code:
//Read records from binary file and displays them on VDU
#include <stdio.h>
#include <ctype.h>
int main() {
FILE *fp;
struct emp {
char name[40];
int age;
float bs;
} e;
fp = fopen("emp.bin", "rb");
if (fp == NULL) {
puts("Cannot open the file.");
return 1;
}
while (fread(&e, sizeof(e), 1, fp) == 1) {
printf("\n%s \t %d \t $%.2f\n", e.name, e.age, e.bs);
}
fclose(fp);
return 0;
}

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