Conversion of strings into numbers and precautions

Conversion of strings into numbers and precautions

Convert a string to a number:

Atoi, atol, and atoll are required for Signed Conversion. Use strtoul and strtoull for unsigned conversion.

(1) Common conversion functions

Converted to signed:

# Include <stdlib. h>

Int atoi (cosnt char * nptr );

Long atol (const char * nptr );

Long atoll (const char * nptr );

Long atoq (const char * nptr );

Long int strtol (const char * nptr, const char ** endptr, int base );

Long int strtoll (const char * nptr, char ** endptr, int base );

Converted to unsigned:

Unsigned long int strtoul (const char * nptr, char ** endptr, int base );

Unsigned long int strtoull (const char * nptr, char ** endptr, int base );

(2) scenario Problems

Unsigned int value = (unsigned int) atoi ("3000000000 ");

Printf ("value = % u", value );

In a 64-bit machine, value = 3000000000. However, in 32-bit machines, value = 2147483647

Because the atoi function is implemented using strtol internally, in atoi, strtol converts "3000000000" to the long type,

In 64-bit machines, long is 8 bytes, the highest bit is the symbol bit, and the data bit is 63 bytes.

In 32-bit machines, long is 4 bytes, the highest byte is the symbol bit, and the data bit is 31 bytes. The Signed Conversion Function strtol truncates "3000000000" to 2147483647 (the maximum number of signed four-byte positive values, that is, the binary number is 0111 1111 1111 1111 1111 1111 1111 1111 ).

Use strtoul to correctly handle the error (valid for the number of 4-byte unsigned characters ).

Similarly, for 8-byte unsigned numbers, strtoull is required. Otherwise, even if atoll is used for conversion, the same problem may occur (either 64-bit or 32-bit ).

The Code is as follows:

Example

12345678910111213141516

/* Strtoull example */# Include <stdio. h>/* Printf, NULL */# Include <stdlib. h>/* Strtoull */IntMain (){CharSzNumbers [] ="250068492 7b06af00 1100011011110101010001100000 0x6fffff";Char* PEnd;Unsigned Long Long IntUlli1, ulli2, ulli3, ulli4; ulli1 = strtoull (szNumbers, & pEnd, 10); // This number is a 10-digit number ulli2 = strtoull (pEnd, & pEnd, 16 ); // The hexadecimal number ulli3 = strtoull (pEnd, & pEnd, 2); // The hexadecimal number ulli4 = strtoull (pEnd, NULL, 0 ); // This number is based on the specified prefix's hexadecimal number printf ("The decimal equivalents are: % llu, % llu, % llu and % llu. \ n", Ulli1, ulli2, ulli3, ulli4 );Return0 ;}

Output:

The decimal equivalents are: 250068492, 2064035584, 208622688 and 7340031.

 

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