How to write an int using fwrite()

Question

Let's say I have a int largeInt = 9999999 and char buffer[100], how can I convert largeInt into a string (I tried buffer = largeInt, doesn't work) and then fwrite() to a file stream myFile?

Now what if I want to write "The large number is (value of largeInt)." to myFile?

Do you want largeInt to be written to the file in binary or as text? — fuz
– fuz, Commented Nov 6, 2015 at 7:36
@Ehsan: Don't worry about small performance differences until you know that you really need the speed, and that you have profiled your program to find where the bottlenecks are. — Thomas Padron-McCarthy
– Thomas Padron-McCarthy, Commented Nov 6, 2015 at 7:40
@Ehsan Which still needs to be done to "convert" the number to a string. — Some programmer dude
– Some programmer dude, Commented Nov 6, 2015 at 7:40

BlackMamba · Accepted Answer · 2015-11-08 17:24:59Z

3

An example :

int largeInt = 9999999;
FILE* f = fopen("wy.txt", "w");
fprintf(f, "%d", largeInt);

Please refer this link:http://www.cplusplus.com/reference/cstdio/fprintf/

If you want use fwrite,

char str[100];
memset(str, '\0', 100);
int largeInt = 9999999;
sprintf(str,"%d",largeInt);

FILE* f = fopen("wy.txt", "wb");
fwrite(str, sizeof(char), strlen(str), f);

edited Nov 8, 2015 at 17:24

user4710450

answered Nov 6, 2015 at 7:53

BlackMamba

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Comments

score 2 · Accepted Answer · 2015-11-06 08:54:21Z

2

You may use the non-standard itoa() function as described here and convert the number to string and then format your sentence using sscanf to format it.

itoa() : Converts an integer value to a null-terminated string using the specified base and stores the result in the array given by str parameter.

Then write the sentence to your file using fwrite.

edited Nov 6, 2015 at 8:54

answered Nov 6, 2015 at 7:44

user4710450

2 Comments

Dylan Czenski Over a year ago

Thank you so much. And from the documentation I noticed that itoa() has a return value, which is a pointer to the resulting null-terminated string, same as parameter string... I wonder why it is designed this way. I thought strings are arrays in C, and arrays don't need to be returned.

Andrew Henle Over a year ago

itoa() is definitely non-standard. See stackoverflow.com/questions/190229/…

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