Convert char to int with blank space in C

Question

I have a char variable such as a = ' 123' or b = '\t123'. So how to convert them into integer? My problem is read form text file contains multi lines of char like a and b. I want to convert them and save to an array. Here is my code:

int main(){
FILE *file_pid;
int i = 0;
int number[100];
char line[20];
    file_pid = fopen("pid.txt","r");
    while(fgets(line, sizeof line, file_pid) != NULL){
         number[i] = atoi(line);
         i++;
    } 
}

Edited: I solved my problem. Many thanks!

What is the target platform? The use of multi-character literals is a relatively uncommon extension. — supercat, Apr 10 '19 at 16:27
Just use `atoi()` or `strto(u)l()`, it will ignore leading whitespace — Ctx, Apr 10 '19 at 16:28
@ĐứcTuấnTrương Too bad. Maybe it would help if you showed a minimal compilable code snippet to reproduce the issue. — Ctx, Apr 10 '19 at 16:43
@ĐứcTuấnTrương The code has several issues, but looks mostly ok. It still isn't complete, however, how is "number" declared? How do you observe that it is not working, since there is no output? — Ctx, Apr 10 '19 at 17:03
Edit your question to show the contents of _pid.txt_ and the output when you execute your program. Note you do not check _fopen_ success — bruno, Apr 10 '19 at 17:08
@bruno Above you write "use one of the atol functions or sscanf". So, how is atol better than atoi? — Ctx, Apr 10 '19 at 17:27
@Ctx sorry, typo, I wanted to say strtol, like in my answer ;-) — bruno, Apr 10 '19 at 17:38

score 0 · Accepted Answer · answered Apr 10 '19 at 16:44

0

you can use atoi() function to directly convert a string into integer. The C library function:

int atoi(const char *str) converts the string argument str to an integer. This function returns the converted integral number as an int value. If no valid conversion could be performed, it returns zero. good part is that it ignores spaces.

you might not want to store multi-character character constant in a character variable. Use character array instead example:

char c[] = " 123"; printf("%d\n", atoi(c));

answered Apr 10 '19 at 16:44

coco97

65
7

is it required to store it in a character variable? – coco97 Apr 10 '19 at 17:00
1

`atoi` is bad. Use `stoi` instead. [Why shouldn't I use atoi()?](https://stackoverflow.com/q/17710018/995714) – phuclv Apr 11 '19 at 12:03

Convert char to int with blank space in C

1 Answers1