integer extraction from string

问题

I have an input argument string const char* s I know that it starts the sequence of chars which are integers representation ,this sequence could be of any length ,including 0. After the integer sequence follows sequence of chars which are not integer representation. for example "23meeting","1h". Is there some (builtin) C function which can extract the integer? For example for "23meeting" such operation could be performed :

int x = needed_function("23meeting"); //results x = 23

Thanks

回答1:

atoi() should work fine for this. It should stop at the first non-numeric character.

int x = atoi("23meeting")

EDIT: A comment implies that atoi() is not thread safe or is deprecated from the language. There is some discussion of the thread safety of this function here:

Why does OSX document atoi/atof as not being threadsafe?

Can someone provide a reference to atoi not being thread safe?

And as far as I can tell atoi() is in C99 which is the latest standard (7.20.1.2).

回答2:

You can iterate through the string and can give the condition to get numbers

num=0;
for(i=0;str[i]!='\0';i++) {
if(str[i]>=48 && str[i]<=57)
 num=num*10+(str[i]-48);
  printf("\n%d",num);
} 

回答3:

Try atoi() or the complete strtol():

int x = atoi("23meeting");
int x = (int)strtol("23meeting", (char **)NULL, 10);

Check the man pages on your system (section 3 in Unix).

回答4:

One way would be to use sscanf:

char *str = "23meeting";
unsigned x;
sscanf(str, "%u", &x);
printf("%u\n", x);

For additional error-checking, though, you'll have to do some additional manual checks.

回答5:

atoi() should do what you want to, although a more robust implementation would use strtol().

来源：https://stackoverflow.com/questions/7842153/integer-extraction-from-string