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- Integer arguments of types ranked lower than
intare promoted toint, ifintcan hold all the values of that type; otherwise they are promoted tounsigned int(the "integer promotions"). - Arguments of type
floatare promoted todouble.
Non-Compliant Code Example (
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Type Interpretation Error)
The C99 printf() function is implemented as a variadic function. This non-compliant code example swaps its null-terminated byte string and integer parameters with respect to how they were specified in the format string. Consequently, the integer is interpreted as a pointer to a null-terminated byte string and dereferenced. This will likely cause the program to abnormally terminate. Note that the error_message pointer is likewise interpreted as an integer.
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const char *error_msg = "Error occurred";
/* ... */
printf("%s:%d", 15, error_msg);
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Compliant Solution (
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Type Interpretation Error)
This compliant solution is formatted so that the specifiers are consistent with their parameters.
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As shown, care must be taken to ensure that the arguments passed to a format string function match up with the supplied format string.
Non-Compliant Code Example (
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Type Alignment Error)
In this non-compliant code example, a type long long integer is incorrectly parsed by the printf() function with a %d specifier. This code may result in data truncation or misrepresentation when the value is extracted from the argument list.
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Because a long long was not interpreted, if the long long uses more bytes for storage, the subsequent format specifier %s is unexpectedly offset, causing unknown data to be used instead of the pointer to the message.
Compliant Solution (
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Type Alignment Error)
This compliant solution adds the length modifier ll to the %d format specifier so that the variadic function parser for printf() extracts the correct number of bytes from the variable argument list for the long long argument.
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