C language determines whether a string is a number

C language determines whether a string is a number

 

It sounds simple to determine whether a string is a number, and the implementation is still a bit difficult. I recently wrote one, as follows:

 

#define IS_BLANK(c) ((c) == ' ' || (c) == '\t')#define IS_DIGIT(c) ((c) >= '0' && (c) <= '9')#define IS_ALPHA(c) ( ((c) >= 'a' && (c) <= 'z') || ((c) >= 'A' && (c) <= 'Z') )#define IS_HEX_DIGIT(c) (((c) >= 'A' && (c) <= 'F') || ((c) >= 'a' && (c) <= 'f'))/* Whether string s is a number.    Returns 0 for non-number, 1 for integer, 2 for hex-integer, 3 for float */int is_number(char * s){int base = 10;char *ptr;int type = 0;if (s==NULL) return 0;ptr = s;/* skip blank */while (IS_BLANK(*ptr)) {ptr++;}/* skip sign */if (*ptr == '-' || *ptr == '+') {ptr++;}/* first char should be digit or dot*/if (IS_DIGIT(*ptr) || ptr[0]=='.') {if (ptr[0]!='.') {/* handle hex numbers */if (ptr[0] == '0' && ptr[1] && (ptr[1] == 'x' || ptr[1] == 'X')) {type = 2;base = 16;ptr += 2;}/* Skip any leading 0s */while (*ptr == '0') {ptr++;}/* Skip digit */while (IS_DIGIT(*ptr) || (base == 16 && IS_HEX_DIGIT(*ptr))) {ptr++;}}/* Handle dot */if (base == 10 && *ptr && ptr[0]=='.') {type = 3;ptr++;}/* Skip digit */while (type==3 && base == 10 && IS_DIGIT(*ptr)) {ptr++;}/* if end with 0, it is number */if (*ptr==0) return (type>0) ? type : 1;elsetype = 0;}return type;}

 

 

The is_number (char *) function determines whether the string is a number. If not, 0 is returned. If it is an integer, return 1. If it is a hexadecimal integer, 2 is returned. If it is a decimal number, 3 is returned.

 

Compile a test program:

 

 

#include 
 
  #include int main(int argc, char**argv){assert( is_number(NULL)  ==0 );assert( is_number("")    ==0 );assert( is_number("9a")  ==0 );assert( is_number("908") ==1 );assert( is_number("-908") ==1 );assert( is_number("+09")  ==1 );assert( is_number("-+9")  ==0 );assert( is_number("  007")  ==1 );assert( is_number("0x9a8F") ==2 );assert( is_number("-0xAB")  ==2 );assert( is_number("-9.380") ==3 );assert( is_number("-0xFF.3") ==0 );printf("test OK\n");}
 

 

Run, "test OK"