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Integer conversions, including implicit and explicit (using a cast), must be guaranteed not to result in lost or misinterpreted data. The only integer type conversions that are guaranteed to be safe for all data values and all possible conforming implementations are conversions of an integral value to a wider type of the same signedness.
Non-Compliant Code Example
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Type range errors, including loss of data (truncation) and loss of sign (sign errors), can occur when converting from an unsigned type to a signed type. The following code is likely to result in a truncation error for almost all implementations:
| Code Block |
|---|
unsigned long int ul = ULONG_MAX; signed char sc; sc = (signed char)ul; /* cast eliminates warning */ |
Compliant Solution
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Validate ranges when converting from an unsigned type to a signed type. The following code, for example, can be used when converting from unsigned long int to a signed char.
| Code Block |
|---|
unsigned long int ul = ULONG_MAX;
signed char sc;
if (ul <= SCHAR_MAX) {
sc = (signed char)ul; /* use cast to eliminate warning */
}
else {
/* handle error condition */
}
|
Non-Compliant Code Example
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Type range errors, including loss of data (truncation) and loss of sign (sign errors), can occur when converting from a signed type to an unsigned type. The following code results in a loss of sign:
| Code Block |
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signed int si = INT_MIN; unsigned int ui; si = (unsigned int)ui; /* cast eliminates warning */ |
Compliant Solution
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Validate ranges when converting from a signed type to an unsigned type. The following code, for example, can be used when converting from signed int to unsigned int.
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NOTE: While unsigned types can usually represent all positive values of the corresponding signed type, this relationship is not guaranteed by the C99 standard.
Non-Compliant Code Example
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A loss of data (truncation) can occur when converting from a signed type to a signed type with less precision. The following code is likely to result in a truncation error for most implementations:
| Code Block |
|---|
signed long int sl = LONG_MAX; signed char sc; sc = (signed char)sl; /* cast eliminates warning */ |
Compliant Solution
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Validate ranges when converting from an unsigned type to a signed type. The following code can be used, for example, to convert from a signed long int to a signed char:
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Conversions from signed types with greater precision to signed types with lesser precision require both the upper and lower bounds to be checked.
Non-Compliant Code Example
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A loss of data (truncation) can occur when converting from an unsigned type to an unsigned type with less precision. The following code is likely to result in a truncation error for most implementations:
| Code Block |
|---|
unsigned long int ul = ULONG_MAX; unsigned char uc; uc = (unsigned char)ul; /* cast eliminates warning */ |
Compliant Solution
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Validate ranges when converting from an unsigned type to a signed type. The following code can be used, for example, to convert from an unsigned long int to an unsigned char:
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